A more thorough explanation:

Definition: Mailable (adjective) refers to a letter or package that is allowed to be sent through a postal service.

Example 1: A postcard is mailable because it meets the size and weight requirements set by the postal service.

Example 2: A package containing hazardous materials is not mailable because it poses a risk to postal workers and the public.

The examples illustrate that mailable items must meet certain criteria set by the postal service in order to be sent through the mail. This includes size, weight, and content restrictions to ensure the safety of postal workers and the public.