Chassis power is the 12v system used to start and run the vehicle. Generally this system is completely separate from house power unless the alternator is used to charge the house batteries.
In the context of this wiki, the main components of the chassis power system are 1) the starting battery - a "thin plate" battery suitable for short duration and high current uses like starting an engine, and 2) the alternator - which creates nominal 12v power when spun by the engine.