If a sign in your hotel says, "Espresso bar is located on the mezzanine," it means that you can get your daily latte fix on the floor of your hotel that's one story above the ground floor.
One meaning of mezzanine is "second floor," although usually the mezzanine level of a building is a partial floor, located between the ground floor and first floor. Another meaning of mezzanine is the lowest of a row of balconies in a theater or symphony hall. You might buy mezzanine tickets to a concert so that you have a good view of the stage. The Latin root of mezzanine is the word medianus, "of the middle."