Earlier quoted context omitted.
Yep, sorry, it's probably a bit confusing. The whole design system is open-source, from its components to also the documentation. You can find it on the GitHub repository: https://github.com/kiwicom/orbit/tree/master/docs
Whole system of what, exactly? Title doesn’t make that clear.
But basically it's a system how to design and develop applications (mostly mobile or frontend). It contains most of the time some visual foundation, standardized components, guidelines etc.