The Associated Content. com provides this description: ACEOs are collectible little pieces of art. An ACEO is always two and one-half inches by three and one-half inches. That is the size of a standard sports trading card. The rule about size is the ONLY rule in the ACEO world. An ACEO can be created in any medium the artist desires: paint, colored pencils, ink, etc. There are even ACEOs made from wood, clay, fabric, and metal.
ACEOs are tiny art works that can be matted and framed to hang on the wall. Many people display their ACEO collections in the same kind of plastic sheets and albums that sports card collectors use. You might slip an ACEO into a greeting card as an extra surprise for a birthday, anniversary, or Christmas.
Sharon's art can be found on her 1000 Markets site. Here are a few more examples that I just love.