Gait
The movement of a horse's foot pattern; walk, trot, canter, lope, rack, amble. Often breed specific.

Gaited horse
A horse with specific styles of gaits or movement. Often breed specific: American Saddlebreds, Morgans, Tennessee Walking Horses. Many gaited horses are born with the gaits and trained to perfect them as they age.

Gallop
A three-beat, high-speed gait, similar but much faster than a lope or canter.

Galls
Sores and swelling on the body.

Galvayne's Groove
A V-shaped groove that appears at the gum line of the corner incisor starting around the age of 10.

Gaskin
The muscle area between the hock and the stifle.    

Geld
To castrate a male horse.

Gelding
A male horse that has been castrated.

Gestation
The time from conception to birth. In horses, around the 345 day mark. 

Girth
The English term for the strap around the belly that holds the saddle in place.

Grade
An unregistered horse of mixed breeding.

Grand Prix
The top or elite of the show jumping and dressage world.

Gray or Grey
A body color of black hair with various amounts of white hair.

Green
A horse or rider with limited experience.

Ground tie
A horse that stands still while the reins or lead rope drop to the ground.

Groundwork
All schooling work done on the ground: leading, manners, handling, longeing, driving.
Article: Basic Groundwork and Saddle work.

Grulla / Grullo
A dun body color with a smoky blueish gray cast. Usually has black mane, tail and legs. Known for a dark dorsal stripes and often 'zebra' stripes on the legs.

Gullet
The area under the fork, swells and pommel of a saddle.

Gut
A horse's stomach.

Gymkhana
Often known as 'games': timed events such as poles/barrels.