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