slight acquaintance
Refers to knowing someone only slightly, not a close relationship. Often used in contexts like 半面識の間柄 (a relationship of slight acquaintance).
I have only a slight acquaintance with him and have never had a deep conversation.
顔見知り implies knowing someone by face, whereas 半面識 suggests knowing only a little about the person, not necessarily by sight.
Compound of 半 (half) and 面識 (acquaintance), literally 'half-acquaintance'. The exact historical derivation is uncertain, but the meaning is transparent from its components.