This document provides definitions and concepts related to the theory of machines. It discusses: 1. The branches of mechanics relevant to machines, including statics, dynamics, kinematics, and kinetics. This course focuses on kinematics - the analysis of motion without forces. 2. How machines are constructed from parts called elements that form pairs and links in kinematic chains and mechanisms. A mechanism becomes a machine when it does work by applying forces. 3. Common mechanisms are examined including four-bar linkages, slider cranks, and bell cranks. Concepts discussed include drivers, cycles, phases, and constrained vs. unconstrained chains.