Epoch

An epoch is a fixed span of blocks or slots that a proof-of-stake protocol uses as its accounting period, the point at which the network tallies validator duties and updates its view of the chain. On Ethereum an epoch is 32 slots of twelve seconds, so roughly six and a half minutes, and validator committees are shuffled each epoch to make targeted collusion harder. Rewards, penalties and the justification and finalisation of checkpoints are all processed at epoch boundaries rather than continuously. Other chains use the term with their own parameters: some measure staking rewards, validator set changes or unbonding delays in epochs, so the unit is protocol-specific rather than universal.