A patient whose treatment needs at least one night's residence in a hospital; a hospitalized patient.
"After his surgery, the doctor decided that John would be an inpatient for two days to monitor his recovery closely."
In plain English: An inpatient is someone who stays overnight at a hospital for treatment instead of going home after each visit.
"The hospital staff needed to find an available bed for another inpatient who had been waiting overnight."
Usage: Use this term to distinguish patients who stay overnight from those treated as outpatients, though "hospitalized" may be preferred in casual conversation. Avoid using it for short-term day procedures where the patient does not sleep at the facility.
The word inpatient combines the prefix in- meaning "inside" with patient. It entered English to describe someone who is admitted and stays inside a hospital for treatment.