Volume
The number of option contracts traded in a contract or underlying during the current session. Volume resets to zero each trading day.
Volume counts every contract that changed hands, whether the trade opened a new position or closed an existing one. It is reported per contract and can be summed across strikes, expirations or the whole option chain for an underlying.
Comparing a contract’s volume with its typical volume, and with its open interest, is one way scanners flag unusual activity. A high volume number alone does not say whether buyers or sellers initiated the trades.
Illustrative example (hypothetical numbers, not a real trade): a contract that usually trades 200 contracts a day prints 6,000 contracts by midday against open interest of 1,500. Volume is 30 times its usual level and four times open interest, which is the kind of reading a scanner flags for a closer look.