REST Representational State Transfer
A design style for APIs that uses HTTP consistently and predictably.
The idea: resources have URLs (/users/42), HTTP methods (GET, POST, PUT, DELETE) say what you want to do with them. No state is held between calls — each request should be understandable in isolation.
Most APIs call themselves REST but follow the rules loosely. Competitors: GraphQL (one endpoint, the client asks for what it wants), gRPC (binary, for internal server-to-server).