A postage meter or franking machine is a mechanical device used to create and apply physical evidence of postage (or franking) to mailed items. Postage meters are regulated by a country's postal authority. A postage meter imprints an amount of postage, functioning as a postage stamp, a cancellation and a dated postmark all in one. The meter stamp serves as proof of payment and eliminates the need for adhesive stamps.

Source: Wikipedia