rain check

Short definition from Wiktionary

Noun

1. 1
   A reissue, at no extra charge, of a ticket for a baseball game or other outdoor event postponed or interrupted because of rain.
2. 2
   A promise or voucher from a merchant to a customer: A (special) price guarantee for a sold-out item or temporarily unavailable service.
3. 3
   A promise or voucher from a merchant to a customer: The promise to make good on any experience that the customer deems unsatisfactory.
4. 4
   An agreement to honor a current offer after its normal expiration: In social interactions, a deferred invitation, or deferred acceptance of an invitation.
5. 5
   Alternative form of rain check.

Verb

1. 1
   Alternative form of raincheck.