Backdoor definition

A surf lingo question. I noticed that surf commentators use the word backdoor to describe going through a peak from the far side of it after the lip has started to tip over. Amoung my group of friends it was entering a tube that had allready formed from the far side and coming out the other side which is a much more difficult thing to do then just to tuck under a lip as it tosses out. I have sucessfully done that only a few times. One day in particular I was surfing a big left called Horners and I was way over from the bowl where most everyone else was taking off. I caught a wave and backdoored the tube (6 foot day so 10-12 foot faces) then caught like 4 more waves and totally got pounded. Paddling back out after the foruth pounding one of the guys who I knew from the group of guys who I knew every one of them paddled over to me and asked me if I was making some of those waves. I said "One out of five so far". He said "OK that's good but if you weren't making any of them we were going to drop in on you." Anyway it is not an easy task to accomplish so I wonder what does backdoor mean to you? What did you learn it to mean?