An ambulance was a automobile used in the 20th century on Earth to transport the sick or injured.
In 1953, Benny Russell was placed in a 1940s Chevrolet ambulance outside the offices of the magazine Incredible Tales of Scientific Wonder. (DS9: "Far Beyond the Stars")
In 2259 of an alternate timeline, an ambulance that was either an aircar or shuttle was parked at the Royal Children's Hospital. (Star Trek Into Darkness)