On the Ethereum 2.0 Beacon chain a slot refers to the 12 second time window during which a new block may or may not be added to either the beacon chain or shards. This 12 second “slot” is the smallest unit of time on Ethereum 2.0 and 32 of these slots comprises an Epoch.
NFT Term
Slot
Definition of Slot from the NFTguild.com glossary.

