Glossary
Slot
A fixed time interval during which one validator is scheduled to propose a block. 12 seconds on Ethereum's beacon chain.
A slot is the smallest unit of time in Ethereum's beacon chain — 12 seconds during which exactly one validator is randomly assigned to propose a block and a committee of others is assigned to attest to it.
Slots can be empty (the proposer was offline, or the network missed the block). Thirty-two slots make an epoch. The slot / epoch abstraction lets the protocol issue duties deterministically in advance, which is critical for proof generation and statelessness.