A mechanism is the system of parts working together that makes something happen or operate. When you flip a light switch, a simple mechanism inside completes an electrical circuit. When you pedal a bicycle, a mechanism of chains, gears, and wheels converts your leg power into forward motion. The mechanism in a music box uses a wound spring and tiny pins to pluck metal teeth and create a melody.

Think of a mechanism as the “how it works” part of any device or process. A clock's mechanism includes springs, gears, and wheels that work together to move the hands at just the right speed. A pencil sharpener has a mechanism of rotating blades that shave wood and graphite into a point. Even a simple door hinge is a mechanism that lets the door swing open and closed.

The word also describes how things happen beyond just machines. Scientists study the mechanisms of disease to understand how illnesses develop in the body. A teacher might explain the mechanism by which plants convert sunlight into food. In these cases, mechanism means the step-by-step process or system that produces a result, whether it involves physical parts, chemical reactions, or biological processes. Understanding mechanisms helps us fix what's broken, improve what works, and invent entirely new solutions.