Open interest is the total number of outstanding derivative contracts, such as options or futures that have not been settled for an asset.
Open interest keeps track of every open position in a particular contract, rather than tracking the total volume traded in it, which may also include netting or closing positions.
Thus, open interest can provide a more accurate picture of a contract's liquidity and interest, identifying whether money flows into the contract are increasing or decreasing.
Open interest decreases when buyers (or holders) and sellers (or writers) of contracts close out more positions than were opened that day