Final answer:
A horse without a documented pedigree, known as a grade horse, can usually be purchased at a lower cost due to the absence of registration with a breed register.
Step-by-step explanation:
A horse that can be bought with a low initial investment because it is not registered with a specific breed register is often referred to as a grade horse. Grade horses do not have documented pedigrees, and therefore, they are typically less expensive than registered breeds. These horses can still be very capable and possess desirable characteristics for riding, work, or companionship, but they do not have the breed verification that often increases the value of a horse.