What is a GraphQL mutation, and how does it genuinely differ from a regular query specifically in terms of properly performing an action that actually genuinely changes data on the server?

While a GraphQL query is specifically used purely for reading and retrieving genuinely existing data without ever actually causing any kind of side effect, a mutation is specifically used whenever you genuinely need to actually create, update, or delete data on the server, and much like a query, a mutation also lets you precisely specify exactly which specific resulting fields you genuinely want returned back once that particular action has actually genuinely completed, such as receiving back a newly created order's own specific generated identifier immediately after successfully placing that order.

mutation {
  createOrder(input: { productId: "123", quantity: 2 }) {
    id
    status
  }
}