Be familiar with sth/sb
to know something or someone well
John is very familiar with software development. He’s been working in IT for 20 years.
I am not very familiar with Han. We’ve just met once.
Do you know Penny (well)?
I was standing right next to her, but she didn't even acknowledge me.
Be familiar to sb
The name of the restaurant was not familiar to me.
I didn't know the name of the restaurant.
Acquaintance /əˈkweɪntəns/ n.
I heard about the job through a mutual acquaintance.