Capital Gain is the Profit (loss) from the sale of securities or other capital assets. Definition from http://www.guardfamily.org/B06/B0601/A0001_D/glossary/bhs04_glossary.html

In finance, a capital gain is profit that is realized from the sale of an asset that was previously purchased at a lower price. The most common capital gains are realized from the sale of stocks, bonds, and property. (If the sale of the asset had yielded a loss rather than a profit, this loss would be called a capital loss.)

Definition from http://en.wikipedia.org/wiki/Capital_gain