ITM = In-the-Money

ITM refers to the moneyness of an option.

Moneyness is a concept referring to the position of the underlying spot price relative to the strike price of the option.

An option is said to be ITM if it possesses intrinsic value. In other words, an option is said to be ITM if it has a positive payout should the option be exercised today.

A call option is said to be ITM if the underlying spot price is above the strike price.
A put option is said to be ITM if the underlying spot price is below the strike price.