A two way speaker refers to how many cones (speakers) are in each box. A woofer is the larger cone and produces the lower and mid tones. A tweeter is the smaller cone which handles the highest tones. An electronic device inside the speaker called a crossover determines what tones go to the woofer and what tones go to the tweeter. Passive simply means there is no internal amplifier in the speakers themselves and they must be driven by an amplifier or more commonly a stereo receiver. In the S15, these are an uncommonly good speaker for developing lows and highs. I highly recommend.