The series of crossover is an electronic circuit in which the point to separate the audio sound frequency. objective that only sound with a frequency range that can be accepted speakers are forwarded. less is more like a filter function, so the speakers work optimally.
2 way or 3 way or else, that determines how many channels would be separated voice. Each channel is handled by a single class of speakers. Eg 3 way, the frequency of sound produced by the head unit, separated by crossover as a low freq (big size distinguished speaker better known as the subwoofer), medium freq (medium speakers), usually in the middle) and hi freq (small speakers I would call a tweeter) Let me better sound and reduce noise.
Schematic 2 Way Speaker Crossover
Schematics for 2 Way - Speaker Crossover circuit Circuit Electronics