Bi-amping means that the speaker can be operated by two amplifiers at the same time, or by a bi-amping-capable AV receiver.
This enables the different chassis (for the treble mid-tone and bass range) to be individually supplied with one signal. Among other things, this could increase the sound performance of a speaker.
Bi-wiring states that the corresponding speaker can be controlled at the same time with two different speaker cables, meaning via separated input sockets for the treble and mid-tone range on one hand, and for the bass range of the frequency switch on the other. This could improve the sound even more. Bi-wiring is the prerequisite for bi-amping.