A component is a self-contained unit of functionality, often in the form of a class or object, that represents a piece of an overall system or application. A subcomponent, on the other hand, is a smaller, simpler component that is used as part of a larger component. A subcomponent is typically used to break down a larger component into smaller, more manageable pieces, and is often used to create reusable building blocks for larger components. In other words, a subcomponent is a component that is used by another component.