Nah, there are two definitions of orb walking; though they do involve casting the orbs effects rather than having them on auto.
The first is the original but is rarely used. Basically, auto attacking causes creeps to aggro on you. However, using orbs does not. Heroes with orbs can therefore attack enemy heroes without taking creep aggro.
The definition that is most often used, and what you are most likely thinking of, is synonymous with 'animation canceling'. Every hero has a bit of lag after an attack, much like in Smash. However, you can cancel this lag by moving right after you attack. Animation canceling is abusing this as a ranged hero to aid in chasing.
Drow can frost arrow, cancel the animation, move, frost arrow, cancel, move, etc. This is much better than just using frost arrows in place, or not canceling after frost arrowing and just following with the auto attack.
Here is a quick video. It's DotA 1 so it might be hard to see, but I'm sure you can find some other videos too.
http://www.youtube.com/watch?v=VbgDcwi08Y0
Edit: Don't want to make another post but since this is my first time in this thread I'll introduce myself. Been playing DotA since DotA 1 and for about 3-4 years now. I'm 'the cat' on steam, message me if you want to play together.