Crypto glossary
Epoch
An epoch is a fixed period in a proof-of-stake chain used to organise validator duties, rewards and finality; on Ethereum it lasts 32 slots, 6.4 minutes.
Proof-of-stake networks divide time into regular intervals so that thousands of validators know when to act. On Ethereum an epoch contains 32 slots of 12 seconds. At the start of each epoch the protocol shuffles validators into committees, assigns block proposers for each slot, and every active validator is expected to attest once during the epoch.
Epochs are also the unit of finality. When two thirds of staked ETH vote for checkpoints in consecutive epochs, earlier blocks become finalised, which normally takes about two epochs, or roughly 13 minutes. Rewards, penalties, validator activations and exits are processed at epoch boundaries, and other chains such as Solana and Cardano use their own, much longer epochs for staking calculations.
The word means different things on different networks. A Solana epoch lasts around two days and a Cardano epoch five days, while Bitcoin has no epochs at all, although ordinal theory calls each period between halvings an epoch. Always check which network a figure refers to.
Example
A new Ethereum validator deposits 32 ETH and waits in the activation queue; it starts attesting at the beginning of a future epoch and its first rewards are credited at the end of that epoch.