ワードアップ英会話 WORD UP ENGLISH CLASS | 日記 | Idioms: "take a rain check"

When you say you want to "take a rain check" on a plan or event, it means you can't go or participate this time, but you'd like to some other time in the future.

For example:

Vincent: Do you want to go get a cup of coffee somewhere?
Jules: Sorry, I'm pretty busy today. Can I take a rain check on that, like maybe next weekend?
Vincent: Okay, sounds good.

Here, Jules is expressing that he'd like to go get coffee sometime, but he can't today, so he'd like to try again next weekend.

The more literal, less idiomatic definition of rain check is a ticket or voucher issued for a rescheduled event when the original event was canceled, often because of rain or other bad weather conditions. In fact, according to Dictionary.com, the expression rain check has its origins in such tickets given for canceled baseball games in the late 1800s.