The phrase 'Raincheck' or 'Rain Check' is used to indicate that you cannot accept an invitation now, but that you’d like to do the same activity sometime in the future.
Example of Use: “I’m too busy to go out to dinner; I’ll have to take a raincheck.”
Interesting fact about Raincheck
Baseball games were sometimes cancelled on account of rain in the days before modern ballparks. When this happened, ticket holders were given a new ticket, called a rain check, to use to attend another game in the future. The practice started in the 1880s.
