When you sell an asset at a higher price than you paid for it, the profit is called a capital gain. The tax you pay on part of that profit is called capital gains tax, or CGT. Here are some posts that discuss this in more detail:

Tax Tuesday: Capital Gains 101

Tax Tuesday: Capital loss, selling crypto and forex gains

Wealthy Maths: Calculate capital gains tax (CGT)

Tax Tuesday: RA allowance and capital gains tax

ETF: Capital gains vs reinvested dividends

Tax Tuesday: Base cost methods for capital gains