traction means propulsion of vichel and traction motor means the motor which propel the our object and it have tractive effort thats why we are saying traction and it is used in railways

dc series motor is used for traction...

Birmingham Motor Traction ended in 2007.

A series motor is employed for traction application which has starting torque and permits intermittent operations by braking, which cannot be expected of a general purpose motor.

DC Traction Motor.