i feel i have a pretty strong idea of what advertising is now. i've dug out this old eddie izzard clip and a couple of quotes i've enjoyed along the way.
"advertising is based on one thing, happiness and you know what happiness is? it's the smell of a new car. it's the freedom from fear. it's the billboard on the side of the road that screams with reassurance that whatever you're doing, it's ok. you are ok."
"the rattling of a stick in a swill bucket."
for those hoping for a more serious definition, i recommend wikipedia.