Hospitalization is the act, or the time, of being taken into a hospital to stay there for treatment — not a short visit to a clinic, and not merely seeing a doctor. If someone needs an operation, or is too ill to go home, that stay is hospitalization. It is a formal, medical, paperwork kind of word; families more often say she is in hospital (British) or she is in the hospital (American). The American spelling is hospitalization; British English often writes hospitalisation. The verb is hospitalize / hospitalise. Though actually, students sometimes use this word for any trip to a hospital, even when the person visits and goes home the same day. That is not how doctors and forms use it.