ambulatory care is the same thing as inpatient care
inpatient (care/unit/ward) - is the one where a patient stays for 24h. outpatient (...) - is the one where a patient spends most of the day (e.g. 8 hours) ambulatory care - is the one where a patient visits their doctor from time to time (e.g. 1-hour appointments every Monday - definitely a case in psychiatry, don't know about other specialties)