"What you see is what you get."
This is from UbuWeb, a great resource on the avant-garde, I really can't recommend it enough.
In the above link, the father of conceptual art lays out the guidelines for his oeuvre.
Here's a great snippet, #8:
"When words such as painting and sculpture are used, they connote a whole tradition and imply a consequent acceptance of this tradition, thus placing limitations on the artist who would be reluctant to make art that goes beyond the limitations."