what is art?

What is art? This seems to be the question asked during the first web art and design lesson. Unfortunately it is a particularly difficult one to answer. To add the extra constraints of 'on the web' narrows the answer field even further.
Gianni pointed out that what needs to be focussed on when deciding whether or not a particular site is art is its intent. If it was built to be a promotional or marketing site then often its intent is not art, but selling, and its treatment is merely lovely design.
An artist or gallery displaying its artwork online is also promotion. The intent of the original is art, but its reproduction deletes this previous ideal.
Unfortunately the internet is a marketing domain, therefore works of art online are few whilst beautifully designed marketing sites abound.