This is the measurement used to define the motor’s power output. In the UK, electric motors are allowed to be sold with an output up to and including 250 watts. Anything above this is not classed as an e-bike and is subject to licence and insurance legislation the same as mopeds.
Voltage is a measurement of potential energy. E-bike batteries are sold in different voltages, ie 36V. The higher the voltage, the more work it can do with fewer amps needed.
Simply put, torque is the amount of rotational power the e-bike motor puts out to turn the wheels and so assist the rider. It’s usually measured in newton-metres (Nm) and the higher the torque, the more acceleration the bike motor can provide.
Newton-metres are a measurement of force multiplied by distance. The torque of an e-bike motor is usually measured in Nm (in the UK). So, for example, if the motor is in the wheel (hub-drive), Nm is the power of the motor in newtons multiplied by the radius of the wheel in metres. A motor that can deliver 50 newtons over 0.62 metres (a 700c wheel, which has a radius of 622mm) would be measured at 31Nm.