There are two basic type of chaps - full or half length.
Full length chaps originate from the USA where they were worn by cowboys to protect the complete leg while working. They consist of two independent leg coverings attached at the waist by a belt and are worn over jodhpurs. Full length chaps are available in a variety of materials including leather, suede and waxed waterproof versions. Full chaps help to keep the legs warm and dry whilst riding which can be particularly useful during the winter.
Half chaps are worn with jodhpur boots and cover the leg from the below the knee to the ankle with a strap that goes under the boot. They are available in a variety of colours and fabrics including suede and leather. As well as offering some protection to the lower leg they also prevent jodhpurs from riding up the lower leg whilst riding.
Gaiters are closely fitting half chaps cut in the traditional riding boot style, most often made of leather.
Many equestrian sporting organisations now allow the wearing of black leather gaiters worn with black jodhpur boots as an acceptable alternative to wearing full length black riding boots during competitive events.