What is Capital Gain?

Legal Definition
A capital gain is a profit that results from a sale of a capital asset, such as stock, bond or real estate, where the sale price exceeds the purchase price. The gain is the difference between a higher selling price and a lower purchase price. Conversely, a capital loss arises if the proceeds from the sale of a capital asset are less than the purchase price.

Capital gains may refer to "investment income" that arises in relation to real assets, such as property; financial assets, such as shares/stocks or bonds; and intangible assets.
-- Wikipedia
Legal Definition
The amount by which the selling price of an asset exceeds the purchase price; the gain is realized when the asset is sold
Legal Definition
These gains are made from the profits from sales of capital assets that is in excess of costs and values.