The physics lab was a laboratory where physics was studied.
Starfleet Academy had a physics lab. In 2367, Wesley Crusher re-programmed the antimatter regulator there to spray serial practical joker Adam Martoni with chili sauce. Robin Lefler wasn't there to witness the incident, but she had friends who mentioned it to her. (TNG: "The Game")
A deleted scene from TOS: "Space Seed" mentioned a crewmember named Hanson who worked in USS Enterprise's physics lab.