Maximum Card

In philately a maximum card (also known as a maxi-card, or maxicard) is a postcard with a postage stamp placed on the picture side of the card where the stamp and card match or are in maximum concordance. The cancellation or postmark is usually related to the image on the front of the card and the stamp.

Not every country issues maximum cards (ie USA does not) and some who do (ie Germany) have only a limited number of releases every year whereas others issue maximum cards for every stamp (ie Australia).

The collecting of maximum cards is known as maximaphily.

...
Wikipedia