Back burner

Meaning:
If and issue is not important or urgent and you plan on putting off finding a solution then you can say you are putting the issue on the back burner. Literally a back burner is the burner on a stove on the backside furthest from the chef.
Example Sentence:
We did not really discuss the issue, we left it on the back burner during the meeting.

Catch-22

Meaning:
A catch-22 is a situation where conflicting rules make the desired outcome impossible. It comes from the novel of the same name by Joseph Heller.
Example Sentence:
For new graduates, it is hard to get a job without experience, but one cannot get experience without a job. It’s a bit of a catch-22.

Baby boomer

Meaning:
A baby boomer is a person born that was born after the second world war when there was a massive increase in births. Baby boomers grew up in the 60s or 70s and are now approaching retirement age.
Example Sentence:
The baby boomers are going to be retiring soon putting a strain on the Social Security system.

Coast is clear

Meaning:
The coast is clear is said when it has been determined that it is now safe to proceed; that there are no obstacles or witnesses to what one is about to do.
Example Sentence:
When he was sure the coast was clear, he left his hiding spot.