Design system

A Design System is a set of interconnected patterns and shared practices coherently organized. Design Systems aid in digital product design and development of products such as apps or websites. They may contain, but are not limited to, pattern libraries, design languages, style guides, coded components, brand languages, and documentation.
It serves as a reference or source of truth that helps the different teams involved (such as designers, developers, copywriters and project managers) to design and build digital products.
Some of the advantages of a design system are:
Notable design systems include Lightning Design System (by Salesforce), Material Design (by Google), Carbon Design System (by IBM), and Fluent Design System (by Microsoft).