user-1: There is a lot of talk on breath, now what is breath? What's the meaning?
Is it form? What of it? Is it an action? Is it a perception? A feeling? How should it be taken, if to be taken, so that it would be used right, focused on it right?
Addition: It should be seen to be encouraged to give answers after own investigations on field, having investigated breath, in and of itself.
(Note: this is not given for exchange, stacks, trade or entertainment but as a means for liberation from this wheel.)

user10712: The reason there is a lot of talk about breath is its intermediary function between voluntary and involuntary personal features in human beings. This is also a reflection on the strong emphasis which it has received as a symbolic or literal reference to subjective essence (spirit, soul).
The biological factors are obvious. As mammals we need respiration to survive as part of our sustained organic process. This is part of what constitutes human experience. We breathe, and this continues or we expire. The variable character of this breathing, however, is the focus of a number of liberation instructions or ideologies ostensibly disclosing meaning and purpose.
The reason that focal practices of the Dharma include attention to breath is its rhythmic, ever-present, and involuntary nature. We may learn to loosen our self-control and begin to enter into a condition of repose (calm reflection).
There is no requirement as to breath's role in doctrine or practice. As part of disciplines such as pranayama it may become an exclusive tool to help one move toward liberation. In certain Buddhist practices it may function as an element of practice while meditating having no influence upon breathing while so doing.

user295: In the context of Anapanasati or Anapanasati Sutta this is the respiratory process of breathing in and out.

FORMATION (SAṄKHĀRA)
Ayya, how many kinds of formation are there?
Avuso Visākha, there are these 3 kinds of formation

bodily formation, kāya,saṅkhāra
verbal formation, vacī,saṅkhāra
thought formation. citta,saṅkhāra
But what, ayya, is bodily formation, what is verbal formation, what is thought
  formation?

Avuso Visākha,

The in-and-out breaths, are bodily formation.
Thinking and pondering are verbal formation.
Perception and feeling are thought formation.

But, ayya,'

why are the in-and-out-breaths bodily formation;
why are thinking and pondering verbal formation;
why are perception and feeling thought formation?

~

The in-and-out-breaths, avuso Visākha—these are states bound up with the body. Therefore, they are bodily formation.
Avuso Visākha, one, having first thought and pondered, then breaks out into speech. Therefore, thinking and pondering are verbal formation.
Perception and feeling—these are mentally-connected states, bound up with the mind. Therefore, perception and feeling are thought formation.


Cūla Vedalla Sutta
So the breath is of bodily formations.
Normal breathing, viz., non-volitional, involuntary, uncontrolled breathing is not an action. Controlled breathing like pranayama, is an action as it is volitional or voluntary. Bening mindful of the respiratory process displaces ignorance once sees clearly the true nature of things through the breath, but the same cannot be said about controlled breathing, hence the reason Buddha abandoned these practices as per Ariyapariyesana Sutta, Mahā Sīha,nāda Sutta, Maha Saccaka Sutta. Controlled breathing is an unskilful action which is rooted in ignorance, hence reaping future conditioning. Non-controlled breathing dissolves formations and does not create new formations hence is skilful action. So controlled and mindful breathing is an action with karmic results. Being unaware of the breath and everything else, i.e., one is not practising any of the 4 foundations of mindfulness (Satipatthana), one is accumulating unskilful actions. When one is aware, i.e., practising any of the 4 foundations of mindfulness (Satipatthana), but not necessarily of the breath but compatible with the Satipatthana Sutta and related Suttas, then one still is accumulating skilful action.
The breath as 2 aspects:

movement of the air element - this aspect of the breath can only be perception - this is sensed by the mind sense door. The air element can only be perceived but not be felt.
touch sensation of the breath - this can be felt and perceived - this is felt by the body sense door and subsequently the mind sense door.

The movement of the breath is a perception. Giri-m-ananda Sutta mentions breath as a perception (sanna).
The perceived aspect of breath meditation is the Samatha part and felt part of the breath meditation is the Vipassana part. When once feels the breath at some point one will see a counterpart sign where you feel the touch. When the perceiving part of the breath meditation becomes stronger one starts seeing a mental image.
Breath meditation covers all 4 foundations of mindfulness (Satipatthana).


First Tetrad: Contemplation of the Body (kāya)

Discerning the in and out breathing (SA 8.10 begins with "he trains" in the first step)
Discerning long or short breaths (Ekottarika Agama 17.1 version adds "warm" and "cool" breaths)
Experiencing the whole body (sabbakāya). Pali versions add "he trains" in this step. Some Samyukta-Agama sutras meanwhile have "bodily-formations" in this step.[12]
Calming bodily formations (kāya-saṃskāra)

Second Tetrad: Contemplation of the Feeling (vedanā)

Experiencing rapture (pīti)[14]
Experiencing pleasure (sukha)
Experiencing mental fabrication (citta-saṃskāra)
Calming mental fabrication

Third Tetrad: Contemplation of the Mind (citta)

Experiencing the mind
Satisfying the mind
Steadying the mind (samādhi)
Releasing the mind

Fourth Tetrad: Contemplation of the Mental Objects (dhammā)

Dwelling on impermanence
Dwelling on dispassion (virāga). SA 8.10 instead has 'eradication'.
Dwelling on cessation (nirodha). SA 8.10 instead has 'dispassion'.
Dwelling on relinquishment (paṭinissaggā). SA 8.10 instead has 'cessation'.



Source: Anapanasati Sutta

-1: <p>There is a lot of talk on breath, now what is breath? What's the meaning?</p>

<p>Is it form? What of it? Is it an action? Is it a perception? A feeling? How should it be taken, if to be taken, so that it would be used right, focused on it right?</p>

<p><strong>Addition: It should be seen to be encouraged to give answers after own investigations on field, having investigated breath, in and of itself.</strong></p>

<p><em>(Note: this is not given for exchange, stacks, trade or entertainment but as a means for liberation from this wheel.)</em></p>
 10712: <p>The reason there is a lot of talk about breath is its intermediary function between voluntary and involuntary personal features in human beings. This is also a reflection on the strong emphasis which it has received as a symbolic or literal reference to subjective essence (spirit, soul).</p>

<p>The biological factors are obvious. As mammals we need respiration to survive as part of our sustained organic process. This is part of what constitutes human experience. We breathe, and this continues or we expire. The variable character of this breathing, however, is the focus of a number of liberation instructions or ideologies ostensibly disclosing meaning and purpose.</p>

<p>The reason that focal practices of the Dharma include attention to breath is its rhythmic, ever-present, and involuntary nature. We may learn to loosen our self-control and begin to enter into a condition of repose (calm reflection).</p>

<p>There is no requirement as to breath's role in doctrine or practice. As part of disciplines such as pranayama it may become an exclusive tool to help one move toward liberation. In certain Buddhist practices it may function as an element of practice while meditating having no influence upon breathing while so doing.</p>
 295: <p>In the context of <a href="https://en.wikipedia.org/wiki/Anapanasati" rel="nofollow noreferrer">Anapanasati</a> or <a href="https://en.wikipedia.org/wiki/Anapanasati_Sutta" rel="nofollow noreferrer">Anapanasati Sutta</a> this is the respiratory process of breathing in and out.</p>

<blockquote>
  <p>FORMATION (SAṄKHĀRA)</p>
  
  <p>Ayya, how many kinds of formation are there?</p>
  
  <p>Avuso Visākha, there are these 3 kinds of formation</p>
  
  <ol>
  <li><p>bodily formation, kāya,saṅkhāra</p></li>
  <li><p>verbal formation, vacī,saṅkhāra</p></li>
  <li><p>thought formation. citta,saṅkhāra</p>
  
  <p>But what, ayya, is bodily formation, what is verbal formation, what is thought
  formation?</p></li>
  </ol>
  
  <p>Avuso Visākha,</p>
  
  <ul>
  <li>The in-and-out breaths, are bodily formation.</li>
  <li>Thinking and pondering are verbal formation.</li>
  <li>Perception and feeling are thought formation.</li>
  </ul>
  
  <p>But, ayya,'</p>
  
  <ul>
  <li><p>why are the in-and-out-breaths bodily formation;</p></li>
  <li><p>why are thinking and pondering verbal formation;</p></li>
  <li><p>why are perception and feeling thought formation?</p></li>
  </ul>
  
  <p>~</p>
  
  <ul>
  <li><p>The in-and-out-breaths, avuso Visākha—these are states bound up with the body. Therefore, they are bodily formation.</p></li>
  <li><p>Avuso Visākha, one, having first thought and pondered, then breaks out into speech. Therefore, thinking and pondering are verbal formation.</p></li>
  <li><p>Perception and feeling—these are mentally-connected states, bound up with the mind. Therefore, perception and feeling are thought formation.</p></li>
  </ul>
</blockquote>

<p><a href="http://www.themindingcentre.org/dharmafarer/wp-content/uploads/2013/04/40a.9-Culavedalla-S-m44-piya.pdf" rel="nofollow noreferrer">Cūla Vedalla Sutta</a></p>

<p>So the breath is of bodily formations.</p>

<p>Normal breathing, viz., non-volitional, involuntary, uncontrolled breathing is not an action. Controlled breathing like pranayama, is an action as it is volitional or voluntary. Bening mindful of the respiratory process displaces ignorance once sees clearly the true nature of things through the breath, but the same cannot be said about controlled breathing, hence the reason Buddha abandoned these practices as per <a href="http://www.themindingcentre.org/dharmafarer/wp-content/uploads/2009/12/1.11-Ariya-Pariyesana-S-m26.pdf" rel="nofollow noreferrer">Ariyapariyesana Sutta</a>, <a href="http://www.themindingcentre.org/dharmafarer/wp-content/uploads/2009/12/1.13-Mahasihanada-S-m12.44-63.pdf" rel="nofollow noreferrer">Mahā Sīha,nāda Sutta</a>, <a href="http://www.themindingcentre.org/dharmafarer/wp-content/uploads/2009/12/1.12-Mahasaccaka-S-m36.17-44.pdf" rel="nofollow noreferrer">Maha Saccaka Sutta</a>. Controlled breathing is an unskilful action which is rooted in ignorance, hence reaping future conditioning. Non-controlled breathing dissolves formations and does not create new formations hence is skilful action. So controlled and mindful breathing is an action with karmic results. Being unaware of the breath and everything else, i.e., one is not practising any of the <a href="https://en.wikipedia.org/wiki/Satipatthan" rel="nofollow noreferrer">4 foundations of mindfulness (Satipatthana)</a>, one is accumulating unskilful actions. When one is aware, i.e., practising any of the <a href="https://en.wikipedia.org/wiki/Satipatthan" rel="nofollow noreferrer">4 foundations of mindfulness (Satipatthana)</a>, but not necessarily of the breath but compatible with the <a href="https://en.wikipedia.org/wiki/Satipatthana_Sutta" rel="nofollow noreferrer">Satipatthana Sutta</a> and related Suttas, then one still is accumulating skilful action.</p>

<p>The breath as 2 aspects:</p>

<ul>
<li>movement of the air element - this aspect of the breath can only be perception - this is sensed by the mind sense door. The air element can only be perceived but not be felt.</li>
<li>touch sensation of the breath - this can be felt and perceived - this is felt by the body sense door and subsequently the mind sense door.</li>
</ul>

<p>The movement of the breath is a perception. <a href="http://www.themindingcentre.org/dharmafarer/wp-content/uploads/2009/12/19.16-Girimananda-S-a10.60-piya.pdf" rel="nofollow noreferrer">Giri-m-ananda Sutta</a> mentions breath as a perception (sanna).</p>

<p>The perceived aspect of breath meditation is the Samatha part and felt part of the breath meditation is the Vipassana part. When once feels the breath at some point one will see a counterpart sign where you feel the touch. When the perceiving part of the breath meditation becomes stronger one starts seeing a mental image.</p>

<p>Breath meditation covers all <a href="https://en.wikipedia.org/wiki/Satipatthan" rel="nofollow noreferrer">4 foundations of mindfulness (Satipatthana)</a>.</p>

<blockquote>
  <ol>
  <li><p>First Tetrad: Contemplation of the Body (kāya)</p>
  
  <ol>
  <li><p>Discerning the in and out breathing (SA 8.10 begins with "he trains" in the first step)</p></li>
  <li><p>Discerning long or short breaths (Ekottarika Agama 17.1 version adds "warm" and "cool" breaths)</p></li>
  <li><p>Experiencing the whole body (sabbakāya). Pali versions add "he trains" in this step. Some Samyukta-Agama sutras meanwhile have "bodily-formations" in this step.[12]</p></li>
  <li><p>Calming bodily formations (kāya-saṃskāra)</p></li>
  </ol></li>
  <li><p>Second Tetrad: Contemplation of the Feeling (vedanā)</p>
  
  <ol>
  <li><p>Experiencing rapture (pīti)[14]</p></li>
  <li><p>Experiencing pleasure (sukha)</p></li>
  <li><p>Experiencing mental fabrication (citta-saṃskāra)</p></li>
  <li><p>Calming mental fabrication</p></li>
  </ol></li>
  <li><p>Third Tetrad: Contemplation of the Mind (citta)</p>
  
  <ol>
  <li><p>Experiencing the mind</p></li>
  <li><p>Satisfying the mind</p></li>
  <li><p>Steadying the mind (samādhi)</p></li>
  <li><p>Releasing the mind</p></li>
  </ol></li>
  <li><p>Fourth Tetrad: Contemplation of the Mental Objects (dhammā)</p>
  
  <ol>
  <li><p>Dwelling on impermanence</p></li>
  <li><p>Dwelling on dispassion (virāga). SA 8.10 instead has 'eradication'.</p></li>
  <li><p>Dwelling on cessation (nirodha). SA 8.10 instead has 'dispassion'.</p></li>
  <li><p>Dwelling on relinquishment (paṭinissaggā). SA 8.10 instead has 'cessation'.</p></li>
  </ol></li>
  </ol>
</blockquote>

<p>Source: <a href="https://en.wikipedia.org/wiki/Anapanasati_Sutta" rel="nofollow noreferrer">Anapanasati Sutta</a></p>
