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.
It's fine if things are targeted! I don't expect all my technical documentation to fully namespace all their ambiguous terms in case a non-engineer shows up. This site is for [D]esigners and that's cool.