Refers to token storage that rewards people for participating in token staking or sometimes crypto campaign, usually a P2E game. The reward pool typically contains a part of the project token, and the project owners or campaigners might decide to fill it consistently to avoid drain.
Example
An example of a reward pool is the DAO reward pool system, which distributes rewards in funds to token stakers—to attract more projects into its ecosystem. You can check out this announcement about it in this @TheDaoMaker tweet.