Hospital-acquired infection: An infection caught while hospitalized. The medical term for a hospital-acquired infection is "nosocomial." Most nosocomial infections are due to bacteria. Since antibiotics are frequently used within hospitals, the types of bacteria and their resistance to antibiotics is different than bacteria outside of the hospital. Nosocomial infections can be serious and difficult to treat.
A nosocomial infection is strictly and specifically an infection "not present or incubating prior to admittance to the hospital, but generally occurring 72 hours after admittance."
The word "nosocomial" is made up of two Greek words. The prefix "noso-" comes from "nosus" meaning disease and "-comial" comes from "komeion" meaning to take care of. Nosocomial could therefore refer to any affliction acquired by a patient while under medical supervision, but it doesn't. It now refers more narrowly to a hospital-acquired infection.