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

# Glossary

> The names HydraDB uses for each scope, and the deprecated aliases you may still see.

## Database

The top-level isolation boundary, typically one per customer, environment, or
workspace. Data in one database is fully separated from every other.

## Collection

A partition *within* a database, typically one per end-user, team, or agent. Omit
it and HydraDB uses the database's default collection.

See [Multi tenancy](/essentials/v2/multi-tenant) for how scoping affects writes
and reads.

## Deprecated aliases

`database` and `collection` were previously called `tenant_id` and
`sub_tenant_id`. Wherever you meet an old name - a request field, a route, a
webhook payload - it is a deprecated alias carrying the same value, and it keeps
working.

| Deprecated          | Canonical             |
| ------------------- | --------------------- |
| `tenant_id`         | `database`            |
| `sub_tenant_id`     | `collection`          |
| `sub_tenant_ids`    | `collections`         |
| `/tenants/…` routes | `/databases/…` routes |

Prefer the canonical names in new integrations. See
[Multi tenancy](/essentials/v2/multi-tenant#7-migrating-from-the-legacy-tenant-and-sub-tenant-fields)
for the full compatibility contract, and [Webhooks](/essentials/v2/webhooks) for
the delivery payload.