Definitions

Resource: Something you want to rate-limit (e.g. requests to an HTTP application, or a single route or entity within that application).

Domain: An identifier for a resource or group of multiple resources. Rate-limiting is performed on a per-domain basis.

Client: An entity that sends requests to a resource.

Client Identifier: Something that identifies a client (e.g. IP address or username).

Gatekeeper: A piece of software that controls access to a resource; it can delay or reject requests to ensure that a client does not send too many requests to the resource (rate limiting).

Master: A piece of software that monitors traffic through the gatekeepers, applies rate limiting logic, and instructs the gatekeepers as to when and whether requests are allowed.

Rule: a formula involving a rate (requests per time period) and a burst (a number of requests which can be made before the rate takes effect). A domain can have zero or more rules; it will throttle a request if any rule says it should be throttled.