Delegated Proof Of Stake (DPoS) is the underlying consensus mechanism of EOS. While anyone can run a node to fully validate the EOS blockchain in a trustless manner, only special, selected entities known as Block Producers (BPs) are allowed to produce blocks and determine the canonical blockchain. Unlike Proof Of Stake (PoS), the validating entities taking part in the consensus process, the BPs are not required to lock up tokens. Instead, individual token holders delegate their share of tokens to their preferred BP candidates. The top 21 candidates ranked by aggregate delegated token stake are selected as the active block producers.
Token holders can change their delegations at any time, and within minutes the selection of the 21 active BPs can automatically change. So the BPs only maintain their privileges for as long as the delegating token holders continue to trust them to carry out their responsibilities.
In DPoS, each active block producer has a limited time window under which they have to publish a new block. Suppose an active BP continually misses their block creation times or consistently produces blocks that are missing expected transactions. In that case, EOS token holders, using their stake, can change their delegations to replace them with better block producers that are on standby.
The primary benefit of having such a consensus mechanism is that the EOS Network can consistently maintain a low latency in transaction processing while minimizing missed blocks due to networking issues by having a relatively stable set of active professional BPs who optimize their infrastructure for good performance.
A secondary benefit is that the 21 active BPs effectively act as representatives of the token holders, which allows them to efficiently reach governance decisions through on-chain multisig approvals for issues such as activating consensus upgrades to enhance the blockchain protocol or adding new features provided by system-managed smart contracts.