Trade-to-trade (T2T) or T segment on BSE is segment in which no intra-day trading is allowed for shares falling in that segment, as each trade results in delivery. Transactions placed in this segment have to be mandatorily settled on gross basis i.e. by taking or giving delivery even if you have bought and sold the shares during the same settlement cycle.

If you buy shares, you must pay the money and take delivery.
If you sell shares, you must give the delivery of shares and you will get money.
If you buy today and sell today and don’t have delivery, then the sell position will go in to auction and you will have to pay heavy penalty.