In blockchain technology, the ledger is the entirety of all immutable/unchangeable data. Consensus must be achieved to agree that, “Yes, this ledger is accurate, we all agree.” Hive has a delegated proof of stake (DPOS) consensus mechanism to achieve consensus.

With DPOS, users on Hive can vote with their Hive Power (HP) on witnesses. Witnesses are block producers on the Hive blockchain. A Hive user is saying, “I support witness X with my HP. I trust witness X to do a good job running the chain.”
DPOS is a voting system to select witnesses, however it is not a democracy where each person or account gets one vote. Instead, voting power is based on how much Hive a user has staked. That is, voting is based on a user's Hive Power (which is staked HIVE, or “HP”). The more HP a user has, the more voting power that user has.