# Glossary

Ten words are defined terms rather than ordinary English, and the Terms of Service
incorporates these ten definitions by reference. They mean the same thing on every page
here, in the Portal, and in that agreement. Other capitalised phrases in these pages —
Scored Call, for a Metered Call that returned a score — are ordinary shorthand built out of
these ten, and the agreement does not incorporate them.

## The ten defined terms

- **Account** — the single record that owns a Balance, its API Keys and its Ledger
  history; every Metered Call is attributed to exactly one Account.

- **API Key** — the credential a request presents so the API can tell which Account the
  call belongs to.

- **Balance** — the number of Credits available on an Account right now, read from the
  Ledger every time it is shown and never cached.

- **Credit** — one unit of prepaid consumption against this API, bought in advance and
  consumed by a Metered Call.

- **Ledger** — the authoritative record of every Credit movement on an Account, where each
  Spend, each Refund and each Balance adjustment appears as its own line item.

- **Metered Call** — a call to a priced endpoint, which consumes a Credit;
  `POST /v1/validate` is not one, because it costs nothing.

- **Refund** — a Credit returned to the Balance after a Metered Call ended in one of the
  ways the [error reference](/errors) publishes as refunded; it is always a Ledger line
  item you can see, and it never exceeds the Spend it reverses.

- **Spend** — the Ledger entry recording that a Metered Call consumed a Credit from the
  Balance.

- **Tier** — the commercial band an Account is on; a Tier affects only the price paid per
  Credit, never the cost of a call.

- **Trace ID** — the identifier every response carries in its `trace-id` header, success or
  failure, and that every refusal repeats in the body as `trace_id`; it is the one handle to
  quote when asking about a particular call.