BIT STRAP is a type of fastener used to secure objects together. It is made up of two parts, a bit and a strap. The bit is a metal loop that fits around the object being secured, while the strap is a flexible material that wraps around the bit and tightens to hold the object in place. The term 'REIN' is a four-letter word meaning 'to restrain or control.' Therefore, BIT STRAP can be defined as a fastener used to restrain or control an object by securing it with a metal loop and a flexible strap.