What is a blockchain slot?
A slot is a scheduled window in which a blockchain validator can produce a block. A slot can pass without producing one.
Version 1
GlossaryA blockchain slot is a scheduled window in which a selected validator can produce a block.
Think of a train timetable. Each departure window belongs to one train, but a scheduled departure can still be missed. On Solana, each slot has a leader, yet some slots are skipped and produce no block.
A little more technical
Solana orders slots sequentially and uses them as part of its network clock. The leader assigned to a slot ingests transactions and can produce at most one block. Shorter target slots let the network attempt block production more often, but they do not guarantee that every transaction reaches a block within one slot.
Common misunderstanding
Slot time is not the same as finality. A transaction can appear in a produced block before the network reaches its strongest confirmation state.
Sources: Solana terminology and SIMD-0525.