What’s an epoch?

An epoch is a period of time defined by a crypto, blockchain or DLT network protocol during which the validator nodes that participate in consensus (the validator set) are fixed. 

When a new epoch begins, the Radix Protocol chooses the new validator set based on the current state of stake delegated to validator nodes at that time.

Further reading:

• Start Here! Radix Staking Introduction
• How long is an epoch on Radix?
• What's the difference between Proof of Stake (PoS) and Delegated Proof of Stake (DPoS)?
• What are Proof of Work and Proof of Stake?