Open interest (OI)
The number of option contracts opened and not yet closed, exercised or expired.
How to read it
Counts positions, not their direction: every contract has a buyer and a seller.
How to use it
Shows where positions are concentrated — strikes that can act as magnets near expiration.
Limitations
Reported once a day.
Also called: open interest, oi, call oi, put oi, call open interest, put open interest.