An acquaintance — someone you know but who is not necessarily a close friend.
昔の知人から久しぶりに連絡が来た。
I received a message from an old acquaintance after a long time.
その店は知人の紹介で知った。
I learned about that shop through an acquaintance's recommendation.
知人を通じて仕事を紹介してもらった。
I was referred to a job through an acquaintance.