German to English Bus/Financial Human Resources Stellenbeschreibung

Gidday.

The job description I'm translating specifies that the person occupying this particular position has to provide some sort of cover for other positions in the same department. It's given as follows:

Vertretung aktiv: Produktmanager anderer Gruppen
Vertretung passiv: Leiter Product Management
Unterstellung: Leiter Product Management
etc.

I get the impression that aktive Vertretung refers to long-term(ish) cover while passive Vertretung is for the odd sick day or day off, but I'm not sure of this.

Has anyone come across these terms before? How might I render them?

Thanks in advance.