1. The total number of options and/or futures contracts that are not closed or delivered on a particular day.2. The number of buy market orders before the stock market opens. 1. A common misconception is that open interest is the same thing as volume of options and futures trades. This is not correct, as demonstrated in the following example:-On January 1, A buys an option, which leaves an open interest and also creates trading volume of 1.-On January 2, C and D create trading volume of 5 and there are also five more options left open.-On January 3, A takes an offsetting position, open interest is reduced by 1 and trading volume is 1.-On January 4, E simply replaces C and open interest does not change, trading volume increases by 5.