According to eBay.com...
WHAT DOES ACEO MEAN?
ACEO stands for Art Card Originals and Editions. They are kissin' cousins of ATC's or Art Trading Cards. Both are by definition cards of artwork measuring 2.5 x 3.5 inches, the same as a standard playing card. ACEO's originated on Ebay, and are a favorite form of art on the world's biggest online auction site.
While purists will tell you an ATC must be traded, never sold, it's perfectly true that an ATC is a sub-set of ACEO's. Just like baseball trading cards, they originally were intended to be swapped but now these attractive and creative cards are a class of collectible for sale. Who knows, in future some ACEO artists may become quite collectible. Even now, some ACEO's from popular artists go for a goodly price.
As to medium, ACEO's come in many forms. Oil, acrylic,watercolor, pastel (infrequently; the medium doesn't lend itself easily to small format and is less durable unless fixed.) Colored pencil work, while sneered at in the "serious" art community, is a very beloved medium for ACEO's and the artists who use these pigmented pencils create some stunning work. Some artists work in pen and ink, and also graphite pencil drawing.
But ACEO's don't just have to be made of standard art mediums. Collage artists do altered cards, digital artists make modified photographs, and fiber artists do beaded, knitted, and stitched cards as well.
The subjects can be as varied as a child's imagination, however animal, especially cat ACEO's are widely collected. Whimsical cards, persiflage, jokes and primitive art abound. Landscape miniatures in oils are particularly prized if skillfully done.
One technique of ACEO artwork is to let the frame tell "part of the story." The challenge of working in a 2.5 x 3.5 inch world can be met if the artist leaves a lot of the subject outside the frame and to the imagination. This is a valid compositional technique in art, and a "must" in ACEO work. Even though a picture may only be the size of a playing card, the actual composition suggested might be quite a few times larger, leaving the undone portions to the mind of the viewer to fill in.
THE ACEO PROFESSIONAL ARTIST COMMUNITY
Many artists display their works on Ebay and they sell them. Type in a search for ACEO and look at the incredible variety of artwork available. While serious artwork abounds on Ebay, and there are many artists with galleries online who are self-representing, ACEO works provide a great venue for selling art to the public, real original art or limited editions at a reasonable starting price.
Ebay hosts various groups that meet to discuss and exchange artwork. Artists and enthusiasts join these groups and trade cards or "challenges" and "dares." A dare comes from one artist and is assigned to another to paint a subject or a theme. This can take the artist out of their comfort zone and is a way to spark imagination and growth.
There are now galleries around the US that display and sell ACEO's, which tells us that this art form is growing in popularity everywhere.
ACEO's AS A HOBBY FOR THE AMATEUR ARTIST
As a hobby, ACEO's are great fun for the amateur artist, and can be cost-effective. While canvas, clayboard and watercolor paper are sometimes quite expensive, working in a small format means many works can be obtained from a standard sheet of fine paper. The constraints of working in small format help sharpen skills in composition and value as well as being a real challenge in portraiture. As you get better as an artist, you may feel it is time to list and sell your work. Then you have become--a professional, if you accept the widely-held definition that a professional artist is one who sells their works for compensation.
ACEO's are a growing passion for many people. People collect by subject matter (cats, horses, dogs, wildlife, landscape, or medium (drawings, oils, acrylics, watercolors, colored pencil, altered media and collage.) There are a number of ways to display the collection. Many people keep the cards in sports-cards albums because the 2.5 x 3.5 inch cards fit perfectly into those sleeves. Other people incorporate them into their scrapbooks. Frames are available that display one or more favorite ACEO's. The frame can be a permanent decoration on the wall or desk, or it can be a changing art gallery, slipping a card in and out of a frame for a change of pace. The accessibility of ACEO's--fine art at a reasonable price, plus the small size make this portable art that fits many lifestyles. And historically, miniatures have been highly prized collectibles, from Persian miniatures, Victorian miniatures to today's incredible variety of cards to collect and display.
ACEO's AND ART ACTIVITIES FOR YOUR FAMILY
For children, ACEO making and collecting can become a rewarding past-time, one that can be done alone or with friends and classmates and family. I suggest that families start their own ACEO time at home. A rainy afternoon spent in creating cards can be a wonderful time of togetherness, sparking imagination and creativity. Have a clothesline artshow at the dollhouse afterwards and admire your results. ACEO's are truly art-for-everyone.