This document provides definitions for common sewing machine parts and functions. It explains what automatic thread tension is and how it works to adjust tension for different fabrics. It also defines other key parts like the bobbin, bobbin case, bobbin winder, buttonholes, feed dogs, foot pedal, free arm, integrated drop feed, needle plate, needle up/down function, presser foot, spool holder, and twin needles. In under 3 sentences, it introduces the main components and features of a sewing machine.