A broad definition of a tool's an entity used to interface between two or more domains that facilitates more effective action of one domain upon the other. The most basic tools are simple machines. For example, a crowbar simply functions as a lever. The further out from the pivot point, the more force's transmitted along the lever. A hammer typically interfaces between the operator's hand and the nail the operator wishes to strike. A telephone's a communication tool that interfaces between two… (More on Tool)