Inpatient care is medical treatment that requires a patient to be formally admitted to a hospital, usually staying at least one night under the care of doctors and nurses. An inpatient is the person who has been admitted.
Outpatient care, by contrast, is treatment where the patient goes home the same day, such as a clinic visit, routine test, or minor procedure. Because modern outpatient clinics handle so much, hospitals generally admit people only when they are seriously ill, injured, or need close monitoring.
Source: Inpatient care, Wikipedia