Options Open Interest (OI) is the total number of options contracts that have been purchased and not yet sold or exercised. It is a measure of the total number of options that are currently outstanding in the market. When a new options contract is bought, it increases the open interest, and when an existing contract is sold or exercised, it decreases the open interest. Open interest can be used to gauge the level of activity in the options market and to get a sense of the sentiment of market participants. For example, a rising open interest may indicate that new money is coming into the market and that traders are bullish on the underlying asset. On the other hand, a falling open interest may indicate that traders are closing out their positions and becoming less optimistic. Open interest is typically reported on a daily basis and can be found in financial news sources and market data providers.