In a comment on a recent post about artist Tara McPherson, Tom Jackson asked "What is Lowbrow art?"
First, a disclaimer: my formal training in art history and criticism consists entirely of one semester-long course in college. And that one ended in the Renaissance. I've managed to pick up a bit here and there about the Academic tradition and Art Deco, but I don't know much after 1940. So bear in mind the lack of expertise in this answer.
The Lowbrow art movement is about fifteen years old and is sometimes traced back to the founding of Juxtapoz magazine in 1994. This movement rejects the distinctions between the fine and commercial arts and the sense that the arts belong to a cultural aristocracy. It could be said to be related to folk art, except that its leaders have actual skill and training. Lowbrow is heavily influenced by pop culture and often exhibits a strong sense of humor and the macabre.
Here are some examples from artists sometimes identified with the Lowbrow movement.
Reading the Tea Leaves by Shag. Acrylic on panel, 2009.
Little Boy Blue by Mark Ryden. Oil on canvas, 2001.
Hope by Shepherd Fairey. Stencil and acrylic on paper, 2008. Now at the Smithsonian.
Pavilion of the Red Clown by Robert Williams.
Leave the Hair and Go Free by Amy Sol. Acrylic on wood panel, 2008.
Self-Defeating by Seonna Hong. Acrylic on canvas, 2007.