Three-way active loudspeakers are pro audio speakers that contain 3 different speakers in one enclosure, as well as a power amplifier module built-in so that an external power amplifier is not needed.
The woofer is there to make the low-end happen. The kick drum, the bass guitar, and a little bit of the human voice is reproduced by the woofer in an average two-way speaker. All the rest of the signal, say 1,500 Hertz and above, is fed to a compression driver that is expected to accurately reproduce the middle and upper frequencies. This is nearly impossible without a huge sacrifice in sound quality. In a two-way loudspeaker, we are simply asking too much from a box that is only capable of doing so much heavy lifting.
In a three-way loudspeaker, we introduce a third driver, one whose job it is to reproduce just the mid-range audio signals. This usually includes most of the human voice, so you get a better reproduction of the human voice from a three-way speaker, than any other pro audio speaker. The added benefit of a three-way speaker is that the high frequencies are less distorted at high volume levels, because the compression driver is not trying to reproduce signals below its optimum operating frequency range.