Complex sentence: Breeching ("britching") refers to a strap around a horse's haunches, that allows it to set back and slow a horse-drawn vehicle, usually hooked to the shafts or pole of the vehicle.
Split into simpler sentences: Breeching ("britching") refers to a strap around a horse's haunches. On a horse harness, it allows a horse to set back and slow a horse-drawn vehicle, usually hooked to the shafts or pole of the vehicle.