[montalbano]

That's a valid broader definition but in practice I find it too broad to be very useful.

[memo_salas]

Suggesting one, using source repository analogy :

Below system level you can harmonize (merge) branches of the same system (repository). At system level you would harmonize repositories - might involve politics I guess

Tree vs forest (more than one root)

Beyond systems level would be organic (system of systems)

Does that make sense ?