What It Means
STBT (Sell Today Buy Tomorrow) is the mirror of BTST — selling a stock you don't yet own today, planning to buy it back the next day to cover the position.
How It Works
Unlike BTST, STBT isn't permitted in India's cash equity segment. Any short sale in cash equity must be squared off — bought back — within the same trading day; retail investors can't carry a short cash-equity position overnight. Shorting is normal and legal overnight in the F&O segment, but that's simply a short futures or options position (see NRML), not what STBT specifically refers to.
Warning
Don't confuse STBT with an overnight short in F&O — STBT names the cash-equity mechanic specifically, and that one is blocked for retail traders in India.