Popping is a party dance and Funkstyle created by Sam Solomon aka Boogaloo Sam, out of Fresno, California in the mid 70's with the West Coast Funk movement.
The quick tensing and releasing of muscles, often the arms,legs,back,chest and neck which creates a POP effect is popping. Designed to be done on beat. see popping
Locking is a funk dance created at the early 70's by Don Campbell There was a dance that was popular at the time called the Funky Chicken. Don Campbell didn`t know how to perform this dance properly because every move he did, he used to "lock" his arms. Then the people would say to him: "Do the Lock, Campbell". He created some more moves and patterns and called his new dance "Campbellocking" or just "Locking" for short. see locking
Locking involves a lot of pauses, wrist rolls, bounces, and points.