A "generator unit" refers to a machine or device that creates electrical energy. It usually runs on gas, diesel, or steam, and its primary purpose is to produce electricity.
In the engine compartment diagram, we see a coolant reservoir for a «motor generator unit,» which confirms the available mild hybrid system. (automobilemag.com)
The engineers focused on making the motor - generator unit as efficient as possible. (thetorquereport.com)
Then, as the vehicle comes to a stop, the motor - generator unit spins the engine, bringing it to a smooth stop — properly positioned for a smooth restart. (thetorquereport.com)