This is not an idiom - it means just what it seems to mean - but is a proverb, or old saying.
If you let someone behave poorly, they will behave very poorly. If you let up on a rule ever so slightly, those who usually follow the rule will throw it out all together.
Make a small concession and they'll take advantage of you. For example, I told her she could borrow the car for one day and she's been gone a week--give an inch! This expression, in slightly different form, was already a proverb in John Heywood's 1546 collection, "Give him an inch and he'll take an ell," and is so well known it is often shortened (as in the example). The use of mile dates from about 1900.
(Proverb) Be generous to someone and the person will demand even more. (Describes someone who will take advantage of you if you are even a little kind to him or her.)
"If you let Mark borrow your tools for this weekend, he'll wind up keeping them for years. Give him an inch and he'll take a mile."
It is not an idiom - it means what it seems to mean. This is a very old proverb (already considered old in the 1500's!). It comes from the fact that some people are greedy. If you give them an inch of something, they'll want even more.
it mean you are about to give birth or tou are full
To keep struggling and not give up.
It means to concede defeat and stop trying.
To give someone the slip means to escape from their attempt to capture you.
The idiom give their all means to do everything you can to accomplish a task.
It means to feel that there is no way to go on and you just want to give up.
It's not really an idiom. It means "what are you thinking about."
It is not an idiom, it means your nose is itching.
RFP is not an idiom. It's an abbreviation.
"Have at it" means "give it a try". Another similar colloquialism or idiom would be, "Go ahead, knock yourself out", or "Go for it".
"Sieve" is not an idiom. See the related link.