user6540: I was wondering as Bitcoin is represented in the public and media as a deflationary currency (for more adept media as payment protocol). Is it really deflationary?
Deflation is described on Wikipedia as:

In economics, deflation is a decrease in the general price level of goods and services ...
  This allows one to buy more goods with the same amount of money over
  time.

Inflation is described on Wikipedia as:

Economists generally believe that high rates of inflation and hyperinflation are caused by >an excessive growth of the money supply.

At the moment there is really an excessive growth of Bitcoin supply - in the past 4 years there was mined over 12 millions of bitcoins and will continue
 with every block rewarded by c. 2140 when all bitcoins are expected to be mined. So there will be only transaction fees as block rewards, which will  end the growth of the units supply. 
Can we consider Bitcoin as inflationary and deflationary currency until 2140, because there are still new bitcoins generated until c. 2140?

user9955: The answer to this question depends on the terminology used. "To inflate" normally means "to increase the volume". "To deflate" is the opposite.
In this sense, bitcoins were inflationary in 2013 (the inflation was ca 15%) and will be inflationary in 2014 as well.
At the same time, bitcoins were undergoing hyperappreciation in 2013 (bitcoin appreciation relative to USD was 5783%).
Also, bitcoins were undergoing hypermonetization in 2013 (bitcoin monetization, i.e., increase in liquidity expressed in USD was 2995%).

user1307: This is a tough question.
I'd consider Bitcoin as being just deflationary. Why?
Because, instead of thinking about mining as "adding new currency", you could consider that mining is just "enabling" more coins each block from the 21 million total coins. Everyone knows that ultimately there will be 21 million coins, just not all of them are spendable.
Quoting Wikipedia on inflation:

In economics, inflation is a persistent increase in the general price level of goods and services in an economy over a period of time.

It's clear that the increase of the amount of Bitcoin in circulation is not persistent. I ends. We all know when and why and how much there will ultimately exist.
That said, why is Bitcoin deflationary. Again quoting Wikipedia:

Deflation occurs when the inflation rate falls below 0% (a negative inflation rate).

One can argue that after the last block reward has been paid, the amount of bitcoins will stay the same. That's not true. Now already, bitcoins are getting lost. People lose bitcoins every day by losing the private keys. So, bitcoins will become scarcer whenever the rate at which people lose them tops the generation rate through mining.
So ultimately, the number of spendable bitcoins will decrease, but firstly, as bitcoins tend to increase in value, people will probably become more careful with them over time. And second, bitcoins can be divided to the order of 10^8, so even when there is only a fraction of the 21 million bitcoins left, people will be able to spend regular amounts using the bitcoin protocol.

user-1: The keyword is "excessive".
Inflation can be related to the supply of money with the quantity theory of money:  
MV = PQ 
Where M is the supply of money, V is the velocity of money, P is prices, and Q is production, all taken as the temporal quotient thus geometrically added. 
Prices can only go up or down.  Judging by the exchange rate, prices in terms of BTC are deflating as no one would pay 3 BTC for a gallon of gasoline as they would at the beginning of 2012 or so; now, they would pay 0.0003 BTC.
Price are deflating because demand for bitcoin is rising as evidenced by the skyrocketing velocity.
So even though the supply is growing, it is not excessive because velocity is growing so much faster.  Actually, the supply of bitcoin should've grown faster during this period, but it is not programmed to do that.
No cryptocurrency is currently programmed for perfect price stability.

6540: <p>I was wondering as Bitcoin is represented in the public and media as a <code>deflationary</code> currency (for more adept media as payment protocol). Is it really deflationary?</p>

<p>Deflation is <a href="http://en.wikipedia.org/wiki/Deflation" rel="nofollow">described on Wikipedia</a> as:</p>

<blockquote>
  <p>In economics, deflation is a decrease in the general price level of goods and services ...
  <strong>This allows one to buy more goods with the same amount of money over
  time.</strong></p>
</blockquote>

<p>Inflation is <a href="http://en.wikipedia.org/wiki/Inflation" rel="nofollow">described on Wikipedia</a> as:</p>

<blockquote>
  <p>Economists generally believe that high rates of inflation and hyperinflation are caused by >an <strong>excessive growth of the money supply</strong>.</p>
</blockquote>

<p>At the moment there is really an excessive growth of Bitcoin supply - in the past 4 years there was mined over <strong>12 millions of bitcoins</strong> and will continue
 with every block rewarded by c. 2140 when all bitcoins are expected to be mined. So there will be only transaction fees as block rewards, which will  end the growth of the units supply. </p>

<p>Can we consider Bitcoin as inflationary and deflationary currency until 2140, because there are still new bitcoins generated until c. 2140?</p>
 9955: <p>The answer to this question depends on the terminology used. "To inflate" normally means "to increase the volume". "To deflate" is the opposite.</p>

<p>In this sense, bitcoins were inflationary in 2013 (the inflation was ca 15%) and will be inflationary in 2014 as well.</p>

<p>At the same time, bitcoins were undergoing hyperappreciation in 2013 (bitcoin appreciation relative to USD was 5783%).</p>

<p>Also, bitcoins were undergoing hypermonetization in 2013 (bitcoin monetization, i.e., increase in liquidity expressed in USD was 2995%).</p>
 1307: <p>This is a tough question.</p>

<p>I'd consider Bitcoin as being just deflationary. Why?</p>

<p>Because, instead of thinking about mining as "adding new currency", you could consider that mining is just "enabling" more coins each block from the 21 million total coins. Everyone knows that ultimately there will be 21 million coins, just not all of them are spendable.</p>

<p>Quoting Wikipedia on inflation:</p>

<blockquote>
  <p>In economics, inflation is a persistent increase in the general price level of goods and services in an economy over a period of time.</p>
</blockquote>

<p>It's clear that the increase of the amount of Bitcoin in circulation is not <em>persistent</em>. I ends. We all know when and why and how much there will ultimately exist.</p>

<p>That said, why is Bitcoin deflationary. Again quoting Wikipedia:</p>

<blockquote>
  <p>Deflation occurs when the inflation rate falls below 0% (a negative inflation rate).</p>
</blockquote>

<p>One can argue that after the last block reward has been paid, the amount of bitcoins will stay the same. That's not true. Now already, bitcoins are getting lost. People lose bitcoins every day by losing the private keys. So, bitcoins will become scarcer whenever the rate at which people lose them tops the generation rate through mining.</p>

<p>So ultimately, the number of spendable bitcoins will decrease, but firstly, as bitcoins tend to increase in value, people will probably become more careful with them over time. And second, bitcoins can be <a href="https://en.bitcoin.it/wiki/Units" rel="nofollow">divided to the order of 10^8</a>, so even when there is only a fraction of the 21 million bitcoins left, people will be able to spend regular amounts using the bitcoin protocol.</p>
 -1: <p>The keyword is "excessive".</p>

<p>Inflation can be related to the supply of money with the quantity theory of money:  </p>

<p><strong><code>MV = PQ</code></strong>  </p>

<p>Where <strong>M</strong> is the supply of money, <strong>V</strong> is the velocity of money, <strong>P</strong> is prices, and <strong>Q</strong> is production, all taken as the temporal quotient thus geometrically added. </p>

<p>Prices can only go up or down.  Judging by the exchange rate, prices in terms of BTC are deflating as no one would pay 3 BTC for a gallon of gasoline as they would at the beginning of 2012 or so; now, they would pay 0.0003 BTC.</p>

<p>Price are deflating because demand for bitcoin is rising as evidenced by the skyrocketing velocity.</p>

<p>So even though the supply is growing, it is not excessive because velocity is growing so much faster.  Actually, the supply of bitcoin should've grown faster during this period, but it is not programmed to do that.</p>

<p>No cryptocurrency is currently programmed for perfect price stability.</p>
