### What is a client? ((#what-is-a-client))

Any unique application, service, or user that authenticates to a HashiCorp
Vault cluster. The client count metric is a combination of entity clients and
non-entity clients.

For billing and consumption, only clients that are active during the billing
period count toward total usage. Clients are only counted once within a billing
period, regardless of how many times that client is active and when that client
authenticates to a cluster, it has unlimited access to that cluster for the
remainder of the billing period.

| Installation type | Billing period
| ----------------- | ---------------
| HCP               | monthly
| Self-managed      | annually

Consult the [clients and entities](/vault/docs/concepts/client-count) overview
for more information on client definitions.

### What is the difference between an entity client, non-entity client, certificate client, and secret sync client? ((#eclient-vs-neclient))

- **Entity clients** map to an active identity.
- **Non-entity clients** map to an active non-entity token.
- **Certificate clients** map to an active ACME PKI certificate.
- **Secret sync clients** map to an actively synced secret.

Consult the [clients and entities](/vault/docs/concepts/client-count) overview
for more information about how Vault determines entity assignments.
