There are 3 large main categories to check when buying a treadmill:
The engine and mechanical treadmill (for motorized carpet racing)
Power is expressed in peak and continuously. The peak power is the maximum power you can reach with the treadmill and continuous power is the maximum power reached by the treadmill for training. It is important to know that over the use of the treadmill will be intense; the power must be increased continuously.
Engine power is expressed in CV. More engine power, the greater the treadmill will be robust, as the peak power and continuous.
The inclination is expressed in %; it allows training in hilly terrain and increases your effort even at a reduced speed. The angle adjustment can be manual or electric depending on the model of treadmill.