Safe HTTP Methods

An HTTP method is safe if it doesn’t alter the state of the server. In other words, a method is safe if it leads to a read-only operation. Several common HTTP methods are safe: GET, HEAD, or OPTIONS. All safe methods are also idempotent, but not all idempotent methods are safe. For example, PUT and DELETE are both idempotent but unsafe.

Idempotent

An HTTP method is idempotent if the intended effect on the server of making a single request is the same as the effect of making several identical requests.

MDN Idempotent MDN Safe HTTP Methods