Volume
The number of option contracts traded during a specific period, typically one day.
Explanation
Volume indicates current trading activity and interest. High volume at specific strikes can signal institutional positioning. Volume relative to open interest shows whether activity is opening new positions or closing existing ones. Volume spikes can precede significant price moves.
Example
The AAPL 150 call has daily volume of 25,000 contracts and open interest of 40,000. The high volume relative to OI suggests active new positioning.