An epoch is a cycle that a blockchain protocol uses to group recurring activities. Its duration and purpose depend on the network: the word does not designate one universal number of blocks, hours, or transactions.
Ethereum's clock
On Ethereum, one epoch contains 32 slots, each lasting 12 seconds. An epoch therefore spans 384 seconds, or 6 minutes 24 seconds. A slot is an opportunity to propose a block. If some slots are missed, the epoch can contain fewer than 32 blocks without its scheduled duration increasing.
Duties and checkpoints
Epochs organize validator attestation duties and consensus accounting, including rewards and penalties. Ethereum also uses epoch boundaries to identify checkpoints for its finality process. Finality requires the appropriate validator votes; the passage of an epoch alone does not finalize every transaction.
Other protocols can use epochs for different schedules or validator-set changes, so Ethereum's timing should not be applied automatically elsewhere.
Reading a staking schedule
A service may describe rewards, activation, or withdrawals in epochs. Check which network's cycle it means and which additional queues or processing rules apply. An epoch ending does not by itself guarantee a reward payment, immediate withdrawal, or a fixed return.