About and on

یه دزس کوتاه اما مفید:

Compare:

-a book for children about Africa and its people

A text book on Africa history

- a conversation about money

A lecture on economics

We use about to talk about ordinary, more general kinds of communications.
On suggests that a book, lecture, talk etc is series or academic, suitable for specialists.
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این هم چند تا اصطلاح انگلیسی

Dig oneself in جا خوش کردن  

Hang fireپا در هوا   

Any port in a storm لنگه کفش کهنه در بیابان نعمت است

Beg the question ماست مالی کردن   

A dead cert رد خور ندارد   

Free-handedدست و دلباز

Mark timeدر جا زدن