Question

What is the origin of the idiom " Take a rain check?"

Answer 1

Something you say when you cannot accept someones invitiation to do something but you want to do it some other time

Answer 2

The origin of idiom "Take a rain check?" is that you will try to do that thing later. Meaning you take a rain check and use it later instead, that is what the idiom "Take a rain check?" means.