noun
medicine for external use; topical medicine
Refers to medications applied to the skin or mucous membranes, such as ointments, creams, and patches, as opposed to internal medicines.
この外用薬は1日2回患部に塗ってください。
Please apply this topical medicine to the affected area twice a day.
内服薬 is medicine taken internally (oral medication), while 外用薬 is applied externally.
Compound of 外用 (がいよう, 'external use') + 薬 (やく, 'medicine').