Explain what the PUT method in REST API means and in which cases it is used.

The PUT method in REST API is used for completely updating a resource or creating it if it does not exist yet. Unlike PATCH, which applies partial changes, PUT replaces the entire resource with the provided data.

Main features of PUT:

• Idempotency: repeated calls with the same data will not change the result.
• Usually used to update an existing object at a known URI.
• If the resource does not exist, the server can create it with the specified URI.

Example: if you have a user with ID 123, a PUT request to /users/123 with the full user description will replace all fields of this user with new values.

PUT is used when you need to guarantee the complete replacement of a resource, rather than partial updates.