An electric thruster is one whose power is furnished by an electric motor or batteries.
The electric thruster may be used as a boat's primary propulsion, as well as for bow or stern thrusters.
The electric thruster may be powered by a wide range of electric motors: AC, DC, monophase, triphase, asynchronous, etc.
The primary factor is the power required for proper thruster performance. Other factors include the thruster's placement, as well as that of the motor.