What is a GraphQL mutation?

A mutation is a write operation in GraphQL — it creates, updates, or deletes data (equivalent to POST/PUT/PATCH/DELETE in REST). Mutations are defined separately from queries in the schema under the Mutation root type. Example mutation definition: type Mutation { createUser(name: String!, email: String!): User! }. Calling it: mutation { createUser(name: "Alice", email: "alice@example.com") { id name } }. Like queries, mutations specify exactly which fields to return after the operation. With variables: mutation CreateUser($name: String!, $email: String!) { createUser(name: $name, email: $email) { id } }. Mutations execute serially (in order) when multiple are sent in one request, unlike query fields which resolve in parallel.