What is an ACEO?

ACEO stands for artist card editions or originals. 

Artist trading cards (or ATCs) are miniature works of art about 2 1⁄2 by 3 1⁄2 inches.  Cards are produced in various media, including dry media (pencils, pens, markers, etc.), wet media (watercolor, acrylic paints, oils), paper media (in the form of collage, papercuts, found objects, etc.) or even metals or fiber. The cards are usually traded or exchanged. When sold, they are usually referred to as art card editions and originals (ACEOs).