> ## Documentation Index
> Fetch the complete documentation index at: https://confidence.spotify.com/llms.txt
> Use this file to discover all available pages before exploring further.

# Entities

> An entity is something that can be uniquely identified and randomized.

The entities represent the things you're experimenting on, like your users.
You can use other entities, like ad, product, or visitor.

Each entity has a unique identifier with a specific data type. For example, if you have a UUID that identifies your users, your primary key type is a string.

## Related Resources

<CardGroup cols={2}>
  <Card title="Create Entities" href="/docs/how-to-guides/create-entity">
    Step-by-step entity creation guide
  </Card>

  <Card title="Entity Relation Tables" href="/docs/metrics/entity-relation-tables">
    Connect different entity types
  </Card>

  <Card title="Assignment Tables" href="/docs/metrics/assignment-tables">
    Configure experiment assignments
  </Card>

  <Card title="Fact Tables" href="/docs/metrics/fact-tables">
    Set up entity measurements
  </Card>
</CardGroup>