As far as I know, technically it means if the Bolton train comes into Victoria, you can use the tram to Piccadilly then the Chester train via Stockport to Altrincham.
In reality, although it is
not valid on trams outside the City Zone, it will usually be accepted by almost all inspectors on Metrolink through from Deansgate-Castlefiled via Sale to Altrincham.
The correct ticket to purchase is a single or return from BOLTON to METROLINK ZONE G.
Correct me if I'm (usually) wrong