In 1965, art critic Barbara Rose wrote an article entitled "ABC Art" for the influential magazine Art in America. In it, she described a growing movement away from the dense representational imagery of abstract expressionism, and a new focus on the "minimal" form of art. Under this new paradigm, simplicity of design, shape, and color led to a lack of obvious emotional cues, which gave the audience more room to bring their own views and open-ended interpretations into the art. She enthusiastically wrote that this was the way of the new age of art, where the art became the audience and the audience the art.
Soon after the article appeared, the term "minimalism" began appearing in art circles throughout America and other parts of the world. The term "ABC art" faded into the art history books, deemed too pejorative by most artists, with its linguistic suggestion of obviousness and amateurism. A few artists embraced it, suggesting that, like a child, their art showed wisdom beyond its surface. One artist, describing the term, said
You think ABC, you don't just see three letters. You think of the alphabet, you think of kindergarten, you think of the smells and sights and sounds of your childhood, you think of blocks and spelling tests and all the things that come with it. All of that from three letters. My work is something like that. I create the dots, and the viewer connects them.
For more info on the art itself, see minimalism.
Source: http://daphne.palomar.edu/mhudelson/StudyGuides/20thCentLate_WA.html.