The recreation room (often abbreviated to rec room) was an area aboard a starship where crew-members could relax and take part in recreational activities while they were off-duty.
In the 23rd century, Constitution-class starships had at least six recreation rooms spaced out across the ship. In 2270, when of the recreation rooms aboard the USS Enterprise was equipped with a holographic projector, which was a move towards the holodecks of the 24th century. Also Four-dimensional chess (TOS episodes: "Charlie X" & "Let That Be Your Last Battlefield"; TAS episode: "The Practical Joker"). (TOS novel: Spock's World) (TOS novel: My Enemy, My Ally)
Chinese Checkers were going to be played (TOS novel: Legacy) while waiting for the survey party to be finalized for Alpha Octavius Four