Definition: to have or get at least partial ownership of a project or business; to get benefits from a project
Examples:
My cousin’s business is growing really fast. He is looking for partners, and asked me if I’d like to join him. Of course, I said yes, because I want a piece of the action.
Cem is angry, because we didn’t invite him to join the project. He likes this business, and he wanted a piece of the action.