To hospitalize someone means to admit them to a hospital for medical treatment. When doctors hospitalize a patient, they decide the person needs more care than they can get at home or in a doctor's office. A broken arm might not require hospitalization, but a serious infection, a complicated surgery, or a bad accident often does.

The decision to hospitalize someone usually means their condition is serious enough to need constant monitoring by doctors and nurses, specialized equipment, or treatments that can't be done anywhere else. Someone might be hospitalized for a few days after an appendix operation, or for weeks while recovering from a major injury.

You might see the word used in news reports: “Three people were hospitalized after the car accident” means they were taken to the hospital and admitted for treatment. The noun form is hospitalization, which refers to the entire hospital stay.