Open Interest
The total number of outstanding option contracts that have not been closed, exercised, or expired.
Explanation
Open interest increases when a new buyer and seller create a new contract and decreases when existing positions are closed. High open interest indicates active trading interest and better liquidity at that strike. Changes in open interest can signal institutional activity or positioning.
Example
The AAPL 150 call has open interest of 45,000 contracts, indicating strong liquidity. A sudden jump of 10,000 contracts may signal a large institutional trade.