Design Language, Design system, product design, website design, digital products, pattern library
Components, like buttons, banners, forms inputs, these are pieces assembled to create a digital product.
Guidance, These are directions and information on how to assemble the components correctly.
Reference Site, This is where the components and guidance are stored.
A design system; It's a combination of all the above and more.
It saves & money; it avoids reputation and gives you consistency since all components are already defined and developed;
It helps the team to collaborate; a design system as shared reference and developers and designers will always speak the same language when referring components.
I would take all the hustle and explain how you can build a timeless design system, but as the saying goes "don't reinvent the wheel" where is the resource designsystemchecklist that will guide you through the whole process.