Wing chun definitly isnt a defensive art, basically the concept that just about my teacher and every site Ive read is:

Teaches the fastest and most efficient way to destroy your opponent (maybe not destroy exactly)

Wing Chun is a offensive art, you constantly push forward, attacking and defending in the same movement, using small powerful wingchun punches instead of big swings, taking your opponent down as fast as possible and making sure he doesnt get up using whatever is in your arsenal, this is one of the problems, organized mma fights you aren't allowed to use everything in your arsenal, cant downward elbow, stomp on their face, sometimes my teach even say if you want kick him in the nutz, because thats what wing chun is, in street whatever you do goes, so wing chun is basically a organized way to do everything possible to take down your opponent and most of the "masters" trained like this (not exactly eye gouging but pretenting too) so theyve spent alot of their time practicing techniques that are illegal in UFC and such. Wing Chun is basically about move forward and pound your opponent more then they pound you, something that is really possible with the techniques wing chun teach you (not the illegal stuff), and its not techniques liek you see in movies and such like "tiger pounce" or "swan kick" its really just basic stuff, doesnt need a fancy name, there are only 3 "forms" in this kung fu, each one teaches a "basic" block or attack you can use.