So I've looked at about 100000 videos to try and really REALLY understand the difference. I came narrowed it down to 2:
Popping: The most significant part of this style is 'hitting'. 'Hitting' or 'ticking' is a sudden quick flexing of the body that makes you kind of jolt. Hince the name popping. Popping incorporates liquid, tutting, the snake, the robot, and a few others.
Locking: Lockings' most significant move is the lock. Its this slouched freeze with your hands slightly in front of you dangling, elbows bent. There are many variations of the lock(a lot of people bend one leg and keep the other straight). Locking is a funky style that keeps its roots firmly planted in the old school music genre (funk, jazz, bebop, artist like James Brown!, etc).