Bi-wiring means using separate runs of speaker cable to the HF and LF terminals on a loudspeaker. The intention is to gain some of the benefits of bi-amping (where each driver is driven by a separate amp) at substantially lower cost. There are two methods of bi-wiring from Cambridge amps.
The first is to connect both LF and HF runs of speaker cable to a single set of terminals on the amp and run them to their respective connections on the loudspeakers. With some smaller Amplifiers, this is the only option as they only have a single set of left and right terminals.
The other option is to connect one set of cables to speaker A and the other to speaker B and run them to their respective terminals on the speakers. This has the advantage that 4mm plug terminations can be used on the cables and it can often be easier to wire a single set of cables to each set of terminals. In all cases, you will need to ensure that both speaker A and speaker B are selected.
The performance benefits of bi-wiring are not clear cut as the hundreds of pages of often vitriolic literature that has been written about it attests. In many cases, the noticeable benefits of bi-wiring are conditional on the system and cables used, and experimenting with different cable and amplifier combinations can offer vastly different results when bi-wiring speakers.
For more information regarding the benefits of Bi-wiring please read this article on cambridgeaudio.com.