BTST basically means Buy Today Sell Tomorrow. It is the process when an investor sells his part of share purchased on the previous date to earn some profit. To understand it completely, you will need to understand what exactly it is. In Indian commodity market, equity settlement is done within 2 working days. So, if you are purchasing a share of Monday, you will get it delivered on Wednesday. However, in meantime, if you want to sell it back before it is being delivered to you; you are free to do so. Say, you bought a share on Monday at 100 per share. On Tuesday, the share price went up to 110. Thus, if you sell the share on Tuesday, you will get the additional profits.