Artist Proofs are not usually meant to be out in the world. The small flaws, usually only things that the artist notices, make them not suitable for the numbered editions and in the "art world" the general thought is that selling them only undervalues the editioned prints. But as an artist, I know how much work I put into them and what's the point of packing them away so they are never being enjoyed? I'm also a consumer and I choose to think of APs as a way to offer a more affordable option of original art. 
 
22"x15". Although this one is not part of an edition, it is printed on the same heavyweight BFK Rives paper, is signed and is suitable for displaying. The AP means Artist Proof.