A block and tackle is a system of two or more pulleys with a rope or cable threaded between them, usually used to lift or pull heavy loads.
The pulleys are assembled together to form blocks and then blocks are paired so that one is fixed and one moves with the load. The rope is threaded, or reeved, through the pulleys to provide mechanical advantage that amplifies that force applied to the rope.
Whether it is used to hoist treasure from a pit or move supplies, when it is a properly secured, a block-and-tackle pulley adds a +5 circumstance bonus on STR checks to lift heavy objects. Securing the pulley requires 1 minute.