API key
An API key is a secret string a service issues you so that requests can be traced back to your account and billed or rate-limited accordingly. Anyone who has the key can act as you against that service, so it is treated as a credential, not a public value.
Why it matters
Most modern services let you scope a key to specific permissions and revoke it independently of your account password. Good practice is one key per app or integration, so a leak only affects that one connection.
Is an API key the same as a password?
Functionally similar, but a key is meant for a program to use, not a person to remember, and it can usually be revoked without changing anything else.
How many API keys does a typical setup need?
Often several, one for each service, model provider, or integration you connect.
Related
Looking for a different way to manage your keys? See the best Claude Code API key manager alternatives, or browse every term in the glossary.