Passive speakers have no built-in power supply or pre-amp capabilities, so they require separate amplifiers or mixers to power them - they are essentially just the speaker cones in a housing cabinet. They also require dedicated speaker cables to be able to receive the signal from an amplifier.
Due to the lack of electronic components, passive speakers tend to be much lighter than active ones, making them much easier to transport. As they are stand-alone, they are also much easier to add to an existing system and replace or even omit if something goes wrong.
Please remember to check any new speakers spec to ensure its impedance and power ratings are compatible with your amplifier or mixer. Incompatible speakers won't perform as well and even risk blowing up!