An increase in value of an asset or investment above the price that was purchased. The difference between the new value and the purchase price is the gain.
A capital loss is the reverse. If the asset or investment decreases in value, below what was paid, the difference is a loss.
Capital gains and losses often carry with it tax implications.
They are often broken down into two categories:
Short-term: assets held less than a year
Long-term: assets held more than a year