Bi-wiring is a connection concept for speaker cabinets. It is a double wiring where two speaker cables are routed from the power amplifier to the speaker cabinet. One cable is connected to the midrange and tweeter, the second to the woofer.
The prerequisite for bi-wiring is that the connections of the tweeter, midrange and woofer are routed to the outside and can be connected there. In this connection concept, the speaker signals are routed to the bi-wiring speaker box, where one cable goes directly to the woofer, the second parallel connection is for the tweeter and midrange. In the speaker cabinet, the speaker signals are frequency-separated for the tweeters, midrange and woofer via a high-pass, band-pass and low-pass. The internal connection cables to the tweeters and the midrange driver should be the same length.
More complex concepts are bi-amping, where the frequency components are already separated in the amplifier, and tri-wiring, where each speaker cabinet is connected with three speaker cables.