Recognizing that this is a problematic definition I'm going go with the following:

Art is expression through a medium which is intended for an audience (not necessary a museum or the public on a grand scale, just that it is intended for the experience of others).

fyi: you might be interested in wiki's definition: "Art refers to a diverse range of human activities, creations, and expressions that are appealing to the senses or emotions of a human individual. "

By that measure I think you could include just about anything as art. I'm being facetious of course, but it's a pretty sloppy definition, I'd say. You can read the rest of it at: http://en.wikipedia.org/wiki/Art

The picture I've added to this entry is from the Lascaux caves that I mentioned in class. I honesty don't know if the above is from the copy or the original (and I'm quite sure what to say about copies vs. originals), but it's worth checking out. Apparently you can take a "virtual tour" here.

-Becca