The expression to 'take a rain check' means to postpone an event or a meeting. This expression is a casual way of telling someone you need to change a prior arrangement or that you need to reschedule.

1. I'm not feeling very well today, do you mind if we take a rain check on our lunch date?
2. Let's take a rain check for now until more people are available to attend the party.

1. I need to take a rain check on our meeting this morning, my flight is earlier than I realised.
2. We need to take a raincheck on this particular campaign. What we had planned might be a little insensitive in this political climate.