Capital Gains Tax

What Does Capital Gains Tax Mean?
A type of tax levied on capital gains incurred by individuals and corporations. Capital gains are the profits that an investor realizes when he or she sells the capital asset for a price that is higher than the purchase price. 

Capital gains taxes are only triggered when an asset is realized, not while it is held by an investor. An investor can own shares that appreciate every year, but the investor does not incur a capital gains tax on the shares until they are sold.

Investopedia explains Capital Gains Tax
Most countries' tax laws provide for some form of capital gains taxes on investors' capital gains, although capital gains tax laws vary from country to country. In the U.S., individuals and corporations are subject to capital gains taxes on their annual net capital gains.

It is important to note that it is net capital gains that are subject to tax because if an investor sells two stocks during the year, one for a profit and an equal one for a loss, the amount of the capital loss incurred on the losing investment will counteract the capital gains from the winning investment.