user157: In some of Ryōkan's poems such as this one he mentions the Buddhas of the three worlds

While I gather firewood and wild grasses on this hill,
the Buddhas of the three worlds
Are also celebrating

Who are the Buddhas and what are the three worlds?

user4722: 
No-form (formless)
Form
Desire

http://www.netplaces.com/buddhism/karma-and-worldview/the-three-realms.htm
Also called

Immaterial (arupa-loka)
Fine Material (rupa-loka)
Sensuous (kama-loka)

http://www.accesstoinsight.org/ptf/dhamma/sagga/loka.html
Since that encompasses the whole totality of the cosmos, the buddhas in question are all the supremely enlightened ones -- clear as day to a purified mindstream.

user289: This phrase here means everywhere. 
Specifically, probably the Trailokya, the realm of desire, form and formlessness.  The realm of desire is hell and earth. The realm of form and formlessness are different types of heavens.
ref: https://en.wikipedia.org/wiki/Trailokya
The 10 realms, 10 directions, a three times are all common stock literary phrases that meant everywhere and everything and all times.
And I've lost track of how many ways I've seen the realms sliced up, into the 4, 6, 10 realms, and now with this question, 3!

157: <p>In some of <a href="http://en.wikipedia.org/wiki/Ry%C5%8Dkan" rel="nofollow">Ryōkan's</a> poems such as this one he mentions the Buddhas of the three worlds</p>

<blockquote>
  <p>While I gather firewood and wild grasses on this hill,</p>
  
  <p>the Buddhas of the three worlds</p>
  
  <p>Are also celebrating</p>
</blockquote>

<p>Who are the Buddhas and what are the three worlds?</p>
 4722: <ol>
<li>No-form (formless)</li>
<li>Form</li>
<li>Desire</li>
</ol>

<p><a href="http://www.netplaces.com/buddhism/karma-and-worldview/the-three-realms.htm" rel="nofollow">http://www.netplaces.com/buddhism/karma-and-worldview/the-three-realms.htm</a></p>

<p>Also called</p>

<ol>
<li>Immaterial (arupa-loka)</li>
<li>Fine Material (rupa-loka)</li>
<li>Sensuous (kama-loka)</li>
</ol>

<p><a href="http://www.accesstoinsight.org/ptf/dhamma/sagga/loka.html" rel="nofollow">http://www.accesstoinsight.org/ptf/dhamma/sagga/loka.html</a></p>

<p>Since that encompasses the whole totality of the cosmos, the buddhas in question are all the supremely enlightened ones -- clear as day to a purified mindstream.</p>
 289: <p>This phrase here means everywhere. </p>

<p>Specifically, probably the Trailokya, the realm of desire, form and formlessness.  The realm of desire is hell and earth. The realm of form and formlessness are different types of heavens.</p>

<p>ref: <a href="https://en.wikipedia.org/wiki/Trailokya" rel="nofollow">https://en.wikipedia.org/wiki/Trailokya</a></p>

<p>The <a href="https://en.wikipedia.org/wiki/Ten_spiritual_realms" rel="nofollow">10 realms</a>, <a href="http://www.tientai.net/teachings/dharma/buddha/10directions.htm" rel="nofollow">10 directions</a>, a <a href="http://www.fodian.net/world/buddhas/3tb/3tba.html" rel="nofollow">three times</a> are all common stock literary phrases that meant everywhere and everything and all times.</p>

<p>And I've lost track of how many ways I've seen the realms sliced up, into the 4, 6, 10 realms, and now with this question, 3!</p>
