Plain English Meaning
One radio and one needle that can show you either an airway course from a VOR station or the runway centerline from a localizer, depending on which frequency you tune in.
Full Definition
A combined navigation receiver mode, or a selectable function on a navigation indicator such as the HSI, that processes signals from either a VOR (VHF Omnidirectional Range) station or a localizer transmitter associated with an ILS approach. Both signals share the same VHF frequency band (108.00–117.95 ), so a single receiver can tune and either of guidance, and the indicator automatically interprets the signal appropriately for course display.