In IBFT 2.0 Proof-of-Authority (PoA) networks such as Palm, validators are nodes that validate transactions and mine blocks. Validators take turns to create the next block. Before inserting the block onto the chain, a super-majority (greater than 66%) of validators must first sign the block.
Validators earn rewards for keeping the network honest. Initially the nodes will be run by key stakeholders and technical partners who also contribute to the Palm network in other ways, e.g. by running infrastructure services, tooling for developers, NFT marketplaces, etc.