What is a resolver function in GraphQL?

A resolver is a function on the server that fetches the data for a specific field in the GraphQL schema. Every field in the schema has a corresponding resolver. When a query arrives, GraphQL executes the resolvers for each requested field in a tree-like fashion, starting from the root (Query). A resolver receives four arguments: parent (the result of the parent resolver), args (field arguments from the query), context (shared object for auth, DB connections), and info (query AST info). If no custom resolver is defined, GraphQL uses a default one that reads the same-named property from the parent object.