What is a "handy" horse?

A handy horse is one that is quick on his feet and turns easily - it's a desirable trait in hunters, jumpers and horses working cattle. Western people often use "catty" to refer to the same trait.

"Handy" is also sometimes used to refer to obstacles added to a hunter course to test the handiness of a horse. In England "Handy Hunter" or "Handy Pony" classes are classes that use obstacles you might come across in the hunting field such as opening and closing gates, crossing narrow bridges, etc.