A pony is a certain kind of small horse that is 14.2 hands or smaller (1.47 m, abbreviated hh) at the withers (the highest point of the back), while a horse is anything taller than 14.2 hh at the withers. The term "pony" can be used generally for any small horse or colt, regardless of its actual measurements.
There are several wild breeds of pony, and these have often been captured and bred for various purposes, especially in Britain and Ireland. These wild breeds along with domestic breeds were used as "pit ponies" hauling loads of coal up from the mines, for freight transport, as children's mounts and for entertainment, and later as competitors and performers in their own right.
Properly trained most ponies can be gentle, and are appropriate mounts for children who are learning to ride, or for adults, as ponies are usually very strong.
Information source: Wikipedia