In Spring Boot, "Put Mapping" is an annotation used to handle HTTP PUT requests in web applications. It allows you to create endpoints in your Spring Boot application that handle the update or replacement of specific resources on the server.

The HTTP PUT method is used to update the information of a resource on the server or create it if it doesn't exist. When a client sends a PUT request to a specific endpoint, the server should process the request and update the corresponding resource with the new data provided in the request body.

When a client sends a PUT request to "/users/123" (for example) with the updated user data, Spring Boot will invoke the updateUser method, passing the value "123" as the id parameter and the updated user data as the updatedUser object. Inside the method, you can process the request and update the user with ID 123 in the database or perform any other necessary actions.

Using the @PutMapping annotation, you can create powerful APIs in your Spring Boot application to handle resource updates or creations efficiently. It's important to design your APIs carefully and consider security measures to ensure that only authorized users can update the resources.