It is called a frog.
if you're looking at the underside of the horse's hoof, you'll see a triangular part called the frog. Be careful around the frog when you're picking the dirt off your horses hoof because that part is very sensitive.
Frog
A horses foot is called the Hoof. The Hoof is the hard part on the bottom of the horses leg. Horses hooves are like our fingernails, actually they are made out of the same thing.
A pad horn
Gray.
The bottom of your foot is called the sole or pad.
the triangular shaped part on the middle underside of a horses hoof
horses and by foot
Mountain goats are equipped with this type of hoof. Equines, as in horses and donkeys, also have this style of foot. The inner soft spongy pad is called a frog.
A callus
Arolium
A horses foot is called a hoof.