Active speakers contain their own amplifier to drive the speaker, which will be matched by impedance and power handling. Some active models contain an amplifer that can also drive another passive speaker (satellite).
The main advantage of this type of system is that there is no need for separate amplifiers, which also means that the system can be expanded by simply adding more active speakers and cascading the signal from one to the next. However, each speaker also requires power from the mains, so this should be considered when planning an active speaker installation.
