ACEO stands for "Art Cards, Editions and Originals". These cards are 3.5 inches by 2.5 inches - the size of a trading card.
The reason for this is that Art Cards were made to be traded. Since they were so small, these "Art Cards" quickly became available for sale at low prices, so EVERYONE could enjoy their own piece of art.
The Art Cards are sold either as originals or editions. If it is an "Edition" or Print, it will be numbered and signed.
Art Cards can come in different mediums and of different subjects. Watercolor, Oil, Acrylic, Colored Pencil, Pastels, Pen and Ink, Collage. These ACEOs come in whatever style of art you can think of; abstract, impressionism, cubism, realism, modern art...
What makes them so great is that you can have your own collection of art, from many different artists, and not spend a lot of money.
Wouldn't it be great to have your own mini work of art and you only paid $5 to $10 for it?