When a horse gallops, it runs very fast so that all four legs are off the ground at the same time. If you gallop a horse, you make it gallop.

If you gallop, you ride a horse that is galloping.

A gallop is a ride on a horse that is galloping.

If something such as a process gallops, it develops very quickly and is often difficult to control.

If you gallop, you run somewhere very quickly.

If you do something at a gallop, you do it very quickly.