About

About

About is a preposition or an adverb.
About as a preposition 
The most common meaning of about as a preposition is ‘on the subject of’ or ‘connected with’:
Do you know anything about cricket?I’m very worried about my brother. He’s not well.

About is not as specific as on.
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Compare:
e.g. He wrote a book about the Spanish Civil War.
about is more general and slightly more informal.

e.g. He wrote a book on Barcelona during the Spanish Civil War.
on focuses on more specific and detailed information and is slightly more form
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There are some words we use with about:
complain, concern, excited, happy and worry:

He never complains about the pain.
Everybody was very concerned about the accident.
I’m very excited about coming to France and I can’t wait to see you.
I’m very happy about my trip.
Please don’t worry about me.
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There are some words we don’t use with about:
aware, consider, description, discuss, experience and mention:

She’s not aware of the rules of the road.
Have you considered changing your career?
Can you give us a description of the bag?
Let’s discuss the new schedule.
They have no experience of looking after children.
She didn’t mention where the keys were.
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We use about as an adverb

We use about as an adverb when we talk about time, number and quantity. About makes the time, number or quantity less specific and more approximate:

specific: Dinner is at six.

approximate: Dinner is about six.
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specific: We moved house three years ago.
approximate:We moved house about three years ago.

About can also be used (though less commonly) as an adverb with a meaning of ‘around’:
I was thinking of all the pollution that’s floating about in the air.Around or round?

Be about to
We use the modal expression be about to as an adjective in the modal expression be about to to refer to something that will happen very soon in the future:
He was about to phone the police.

By Cambridge