A cachet (pronounced ka-shay) is a text or design which has significance to the particular stamp on the First Day Cover (FDC). The cachet can be engraved, printed, stamped, hand drawn, painted or pasted-on, or a combination of these. The cachet thus enhances the meaning and appearance of the Cover. Cachets are usually on the left front of the envelope but can cover the entire front of the cover, or in some cases, both the front and back.

Cacheted covers are attractive and unique items to add to a collection, due to the educational and historical information depicted. Some are produced in small quantities, resulting in future high demand and increased value.

Collecting FDC's with cachets has become a specialized philatelic hobby, which has had an upsurge of interest recently. A cacheted cover is more informative than just a stamp. When examined years later, the significance of that time, person or event is easily remembered. Famous people, postal history, significant milestones and battles are just a few examples. As found in any philatelic area, cacheted FDC's have many varieties and subdivisions.