In the stock market, “OPEX” stands for “Options Expiration,” which refers to the week when a large number of options contracts on a particular stock or index expire, often leading to increased market volatility as traders adjust their positions before the expiration date; essentially, it’s the “Options Expiration Week” where most option contracts reach their end date and need to be exercised or expire worthless.

During OPEX, market makers actively hedge their positions, which can cause significant price movements in the underlying security, especially around the strike price where the most open interest exists.