First Day of Issue
USPS issues each new stamp on a specific date and in a city which is chosen for its topical relationship to the stamp. The envelope with the cancel is called a First Day Cover. On the very next day, the stamp is put up for sale at all other post offices nationwide. This makes the envelopes that were canceled on the First Day of Issue more rare and thus, more collectible.
AP (Artist's Proof)
Artist's proofs are used to work out the design and coloration for each edition, and each proof is slightly different. Before I begin a new series based on a particular stamp, I do 1-10 artist's proofs which are individually unique in design and color.
APC (Artist's Private Collection)
Artist's proofs created for my own private collection.
Printed/Hand Painted
A cachet (illustration) that is printed onto the cover (envelope) and then painted or colored by hand.
HandDrawn/Hand Painted
A cachet (illustration) that is applied to a cover (envelope) completely by hand with pen, pencil, brush, etc. Each cachet is made individually and is an original. This makes it more rare as it requires more time to produce.