Art Card Editions and Originals (ACEO) are miniature works of art, size 2,5 x 3,5 inches (6,4 x 8,9 cm). ACEO are trading cards (sometimes called as ATC = Artist trading cards) so they are usually traded or exchanged between artists. They have to be produced in traditional media, not PC work. By traditional media I mean: dry media (pencils, pens, markers, etc.), wet media (watercolor, acrylic paints, etc.), paper media (in the form of collage, papercuts, found objects, etc.) or even metals or fiber.
When you start to create ACEOs It's really hard to fit in that tiny piece of paper . I'm still learning :3.