It's another way of saying you're lost - as if you are out at sea where there are no landmarks to find your way. This can be physically lost or figuratively lost, as in you don't know something.
Another idiom that means the same thing would be "all at sea."
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.
It means to be stuck between two equally horrible choices - as if you were in between Satan and the bottomless ocean, with nowhere else to go."Between the devil and the deep blue sea" is an idiom meaning a dilemma-to choose between two undesirable situations
"Sieve" is not an idiom. See the related link.
It's not an idiom. It means the tip of your nostril.
idiom means expression like a page in a book
It is an idiom. It is referring to the large quantity of faces, not literally a sea of heads.
This is not an idiom. It is a measurement. $100,000 is how you write it in numbers.
Simply its mean a bully.
The idiom your blood is boiling usually means that you are mad/furious.