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Could some one please tell me when to use the word "Off"? What is the meaning of it?

1) Commas are also used to set off interrupting words or descriptive expressions

Other words are RipOff, sendoff, Putoff, Turnoff
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Hi,

Could some one please tell me when to use the word "Off"? What is the meaning of it?

The pencil fell off the table. The basic idea of 'off' here is that the pencil becomes 'away from' the table. It's the same idea with your expressions.

1) Commas are also used to set off interrupting words or descriptive expressions Commas separate (ie move away) the words/expressions from the rest of the sentence. This makes the sentence easier for the reader to understand.

Other words are RipOff I steal your money (move it away from you)
, sendoff You leave, you move away from me
, Putoff, I cause you not to like something, I 'move your mind away from it'.
Turnoff Similar to put off.

These expressions are quite idiomatic, so don't try to invent your own.

Best wishes, Clive
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Could some one please tell me when to use the word "Off"?
The usage you are concerned about is the use of 'off' in phrasal verbs. The particle 'off' has no definite and fixed meaning. You look up the whole phrasal verb in the dictionary. Look up 'set off', not just 'set' or 'off'. They go together as a unit. Same for 'rip off', 'send off', 'put off', and 'turn off'.

'rip off' is completely idiomatic. 'off' here very vaguely suggests 'separation'.
'off' in 'send off' suggests 'away', 'moving away from the speaker'.
'off' in 'put off' suggests 'later', 'more distant in time' in one of the meanings of 'put off'.
'off' in 'turn off' suggests 'not operational', 'not in effect'.

CJ
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Use of off
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AnonymousUse of off
It seems to me that you are asking the same question that has already been asked and answered in this thread.

See a dictionary for the many uses of "off" if you need further information.
You can start here: http://onelook.com/?w=off&ls=a

CJ