The main difference between a 2-way and a 3-way PA speaker is the number of drivers or speakers used to produce sound.
A 2-way PA speaker typically has two drivers: a woofer for low frequencies and a tweeter for high frequencies. These two drivers are each responsible for reproducing a range of frequencies, with the woofer handling the bass and midrange frequencies and the tweeter handling the high frequencies.
A 3-way PA speaker, on the other hand, has three drivers: a woofer for low frequencies, a midrange driver for midrange frequencies, and a tweeter for high frequencies.