From Halopedia, the Halo wiki
Medical tents are UNSC structures, used as shelters for offering emergency medical treatment for personnel in the battlefield. They are shaped like large tunnel tents, open at both ends. They also have small windows on both sides. Unlike conventional tents, they are apparently made of metal or a composite material, and have a metal floor.
Another kind of medical station was used by Liang-Dortmund miners in Meridian Station, Meridian. When the colony was attacked by Prometheans in 2558, it was used to offer emergency medical treatment to wounded miners. The shelter was visited by Fireteam Osiris during their intel gathering, which led them to learn about Apogee Station.