The recent beta notes mention:
Split Themes and Components
Continuing our work to improve Discourse theming we’ve started to split themes and components. Each customization is either a theme or a component, it cannot be both. Users are now prompted to choose between a theme or a component when it is created. Note: splitting themes and components is ongoing and more changes will follow in Discourse 2.2.
I am not sure what that means yet, but I noticed they are using similar terminology, and could possibly mean the same thing as how we use them. 