What is a equestrian club?

Answer 1

A horse course, i.e. where you learn to ride. It can also be the level at which you enter a showjumping competition. Additionally it could mean the Equites, a hereditary caste of ancient Romans.

Answer 2

It can refer to the ancient Roman class largely composed of the cavalry. It can also mean a group of people learning to ride, or one of the levels at which you can enter a showjumping competition.