On MIRA HQ, MedBay is a medium-sized room that contains a scanner and seven futuristic hospital beds. It houses two tasks and a vent that directly leads to Locker Room and Balcony.
On Polus, MedBay is a medium-sized room that is only mentioned in tasks. Otherwise, it is encompassed by Laboratory. It contains a scanner and hospital beds. The beds look like they have a table next to them. It also has two tasks in it.
On The Skeld, there is a vent in the bottom-left corner of MedBay that leads to Security and Electrical. Its most common usage is for traveling through a vent entered in Electrical, but entering the vent in MedBay can be useful.
On The Skeld, the top-left bed has what looks to be a folded blanket in addition to a pillow, while the others have only one pillow. This could mean one of the Crewmates at some point was ill, though it is not confirmed, and it is unknown as to who may have been ill.
On The Skeld, there is a Security camera outside MedBay. A Crewmate watching the cameras can easily deduce if someone is An Impostor by seeing if someone leaves but never went in or vice versa, hinting that the player entered MedBay via the vent in Electrical.
MedBay's name is a portmanteau of "medical bay."
On The Airship, whether or not MedBay is present is unknown. However, a location of a similar name, Medical, is present.