Beginner riders have little or no experience. A beginner’s experience is likely limited to walking on a trail ride or one or two beginner lessons. Beginner riders have not yet learned the ability to correctly guide the horse with their aids.
Novice riders have some basic experience with horses. They have possibly had a few lessons, maybe even owned a horse as a child or recently or taken several lessons. This rider can mount and walk off unassisted. They know the basics on how to ask the horse to move forward, turn and stop. They may also be able to even trot or canter on a very smooth, well trained horse. A novice rider will generally not know how to saddle and bridle a horse by themselves.
An intermediate rider can catch, halter, groom, saddle and bridle a horse by themselves. In the saddle their seat is secure, can trot without bouncing and are comfortable in a slow canter on a gentle, well trained horse. An intermediate rider does not apply unintentional aids to the horse when they lose balance or become unseated.
An experienced rider will ride regularly each week and have had years of riding instruction. Most advanced riders have ridden in their childhood and competed successfully. They will ride with an independent seat, have soft hands and ability to work with horses of any age and background comfortably.
A professional rider is making their living in the equine world either competing, training or educating. They will have a deep understanding of horse behaviour and ability to handle a green horse in open country.