A participant in a Proof of Stake (or similar) system who proposes and attests to blocks, often bonded by a stake.
Validators run nodes that participate in consensus by proposing blocks and attesting to others’ blocks. They usually lock up a stake that can be penalized for misbehavior or downtime.
"A validator with 32 ETH joins the active set, earning rewards for correct attestations and risking slashing if signing conflicting messages."
All terms and definitions may update as the Cryptionary improves.