Definition of Lead: A lope is a three-beat gait. When the horse is loping in the right lead, the footfall pattern is left hind (beat one), right hind and left fore almost simultaneously (beat two), right fore (beat three). The right legs will be reaching the farthest forward and the horse is loping in the right lead.
Definition of Lead Change: A horse changes leads when he changes from one lead to the other lead between two strides in the air at a lope. That is, from right lead to left lead or vice-versa.
The counter canter is an excellent tool for teaching a horse to change leads because, again, I take advantage of his desire to be comfortable. He already knows how to lope in the lead of my choice but the counter canter is not as comfortable – a lead change will put him the lead that is most comfortable on a circle. Note: I do not practice counter canter forever and ever or he may learn it so well that he becomes too comfortable and doesn’t want to change!)