What is open interest OI…?
From the open interest chapter on varsity
Open Interest (OI) is a number that tells you how many futures (or Options) contracts are currently outstanding (open) in the market. Remember that there are always 2 sides to a trade – a buyer and a seller. Let us say the seller sells 1 contract to the buyer. The buyer is said to be long on the contract and the seller is said to be short on the same contract. The open interest in this case is said to be 1.
Open Interest represents the number of outstanding contracts for Future and Option contracts. For Options, every strike price of Option contract has an individual Open Interest value. It can also be defined as the total number of Future or Option contracts that has not been squared off. Open Interest tends to zero value at the expiry day of derivatives market as every one squares off their open positions.