Be familiar with sth/sb

（某人）很了解某人/通晓某件事情

to know something or someone well

John is very familiar with software development. He’s been working in IT for 20 years.

John很了解软件开发。他做IT已经有20年了。

I am not very familiar with Han. We’ve just met once.

我对Han不是太了解。我们只见过一次。

Know 认识(程度可深可浅)

Do you know Penny (well)?

你认识Penny吗？

Acknowledge

(通过招手、微笑等) 打招呼/示意

I was standing right next to her, but she didn't even acknowledge me.

我就站在她身边，但她根本就没有向我打招呼。

Be familiar to sb

(某事)对某人来讲熟悉

似曾相识/见过/听过/闻过

The name of the restaurant was not familiar to me.

I didn't know the name of the restaurant.

这个餐馆的名字我没听过。

Acquaintance /əˈkweɪntəns/ n.

泛泛之交；熟人

I heard about the job through a mutual acquaintance.

我是从一个朋友的熟人那了解到这个工作机会的。