In GraphQL, a schema is the backbone of your API—it defines the structure, functionality, and types of data that clients can query, mutate, or subscribe to. The schema acts as a contract between the client and server, ensuring that both parties understand what data is available, how it can be manipulated, and the relationships between various data types.
- The schema is made up of types, which describe the shape of data.
 - Fields within types specify what data can be requested and returned.
 - The schema is typically written in Schema Definition Language (SDL), which is a syntax designed specifically for defining GraphQL schemas.