Definitions for "open interest"
The total number of futures contracts or option contracts that have not yet been exercised, expired, or fulfilled by delivery.
The cumulative total of all option contracts of a particular series sold, but not yet repurchased or exercised.
The number of outstanding obligations on an exchange-traded contract, usually a good indicator of commercial interest. There will always be an equal number of outstanding buy and sell obligations since these commitments represent completed deals.