Capital gain means any gain or profit you get by selling or transferring a capital asset. These include stocks, bonds, orreal estate. Capital gain only comes into play when you sell such an asset at a price that is higher than what you paid for it. Capital gain is considered in taxation under the head of income which is called capital gains tax.
For instance, say you bought a 10 shares at a price of ₹25 and sold it for ₹55. In this case, you make a profit of (55 – 25) ₹30 on each share, which is referred as your capital gain.