What is Relayer (0x)?

Relayers are 0x decentralized exchange (DEX) users who host off-chain order books, list buy and sell orders, and charge transaction fees. Relayers do not act as a trusted intermediary on the 0x platform, nor do they execute trades, however, their main purpose is to host order books externally to the 0x platform. Relayers help traders find counter-parties (other participants that transact within the network) and cryptographically move orders between them.