(FINANCE) the increase in wealth that goes to the owner of a financial asset when it increases in value. If you buy a share of stock, and the share increases in value, then you have capital gains whether you have sold it or not.
If you sell the stock at the higher price, you have made money on the transaction and have "realized capital gains." If you hang onto the asset in the hopes its value will increase even more, you have "unrealized capital gains."
For owners of stocks, wealth can come in the form of capital gains or dividends. For owners of gold, the only benefit comes from capital gains. This is why gold is usually not a good investment.