An artists proof is part of a limited edition run of prints. Normally low in number they can be marked either just AP or AP/7 and can be signed or unsigned.
These prints are produced before the limited edition run as test prints and are used by the artists to ensure the print is just how they want it so they may vary slightly from the limited edition run.
Artist proofs are often seen as more valuable as they are fewer in number and can be more unique.
