user109: If White will just get a pawn back at no cost, why is the Queens Gambit a Gambit?  Is it for historical reasons or something else?

user924: I think that it's just because it looks like a mirror version of the King's Gambit, nothing more.

user2001: 
A Gambit is a chess opening where a pawn is sacrificed in order to grab the initiative.

The Queen's Gambit is called a Gambit because White sacrifices the c-pawn in order to get a better control over the center.
[FEN ""]
1.d4 d5 2.c4 dxc4

After Black has accepted the pawn with dxc4, the consequence is pretty clear i.e., without a pawn on d5 Black has less control over the center squares e4 and d5. White can use this fact and soon play e2-e4, Nb1-c3 and Bf1-c4 to control these squares.
Practice has shown that accepting the gambit is not the best option for Black. Therefore, many opening systems have been developed where the gambit could be declined, mainly using 2. ..e6 or 2. ..c6.

user652: The fact that a gambit involves a sacrifice in no way means that the sacrifice is permanent. Very few mainline gambit openings for White leave the gambit player with no means of retaking his material.
While Wikipedia does not necessarily make the distinction between a gambit and a sacrifice, I would contend that there is a difference:

A sacrifice is intended as a permanent loss in material in exchange for a superior position.
A gambit is a temporary loss to hasten development or secure a position. 

Based on this understanding, there is no reason NOT to consider the Queen's Gambit as a true gambit, unless you wish to state arbitrarily that there must be more than X number of plies between the loss and the subsequent regaining.

109: <p>If White will just get a pawn back at no cost, why is the <code>Queens Gambit</code> a <code>Gambit</code>?  Is it for historical reasons or something else?</p>
 924: <p>I think that it's just because it looks like a mirror version of the King's Gambit, nothing more.</p>
 2001: <blockquote>
  <p>A Gambit is a chess opening where <em>a pawn is sacrificed in order to grab the initiative</em>.</p>
</blockquote>

<p>The Queen's Gambit is called a Gambit because White sacrifices the <code>c-pawn</code> in order to get a better control over the center.</p>

<pre><code>[FEN ""]
1.d4 d5 2.c4 dxc4
</code></pre>

<p>After Black has accepted the pawn with <code>dxc4</code>, the consequence is pretty clear i.e., without a pawn on <code>d5</code> Black has less control over the center squares <code>e4</code> and <code>d5</code>. White can use this fact and soon play <code>e2-e4</code>, <code>Nb1-c3</code> and <code>Bf1-c4</code> to control these squares.</p>

<p>Practice has shown that <em>accepting the gambit is not the best option for Black</em>. Therefore, many opening systems have been developed where the gambit could be declined, mainly using <code>2. ..e6</code> or <code>2. ..c6</code>.</p>
 652: <p>The fact that a gambit involves a sacrifice in no way means that the sacrifice is permanent. Very few mainline gambit openings for White leave the gambit player with no means of retaking his material.</p>

<p>While <a href="https://en.wikipedia.org/wiki/Gambit_%28chess%29" rel="noreferrer">Wikipedia</a> does not necessarily make the distinction between a gambit and a sacrifice, I would contend that there is a difference:</p>

<ul>
<li><p>A sacrifice is intended as a permanent loss in material in exchange for a superior position.</p></li>
<li><p>A gambit is a temporary loss to hasten development or secure a position. </p></li>
</ul>

<p>Based on this understanding, there is no reason NOT to consider the Queen's Gambit as a true gambit, unless you wish to state arbitrarily that there must be more than X number of plies between the loss and the subsequent regaining.</p>
