In GraphQL, a resolver is a function that is responsible for fetching the data for a field in a query or mutation. Resolvers are defined in the schema and are executed by the GraphQL server when a query or mutation is received.
A synchronous resolver is a type of resolver that runs and completes its execution before returning any value. It directly returns the result of the computation, without waiting for any external event such as a database query or a third-party API call.