Torque wrench is a tool used to apply a specific, measured amount of rotational force (torque) to a fastener, like a bolt or nut, ensuring it's tightened to the correct specification. This prevents overtightening, which can damage threads or break the fastener, and undertightening, which can cause the fastener to loosen. Torque wrenches are crucial in various applications, from automotive and industrial maintenance to DIY projects, where precise tightening is necessary for safety and proper function.