Actually it is both. But you don't need a special language for that. In Delphi as an example it is similar to a class but you need a few additional data. You need an icon to represent the component in the component palette as an example.

I bought many components. It can be a library of internet functions, it can be a complete word processor or just a zip compression component including reading and writing to files. These components have to work indepentently to fit to each project. So they are some kind of an independent package of a single class or even of a complete program containing many classes or no class at all, except the component wrapper class.

So a component is an external addition to extend the functionality of your software. Game developers often use very small components to even extend single classes while other developers try to use complex components to design a complete software architecture from it, sometimes even for drag and drop programming with the help of a visual editor.