Explain the term “synchronous running” with reference to a three phase system?

The rotating magnetic field in the stator and the rotating rotor are locked together and running at the synchronous speed [speed (rpm)=(120*frequency (Hz))/(number of poles)]. Unlike, the asynchronous machines the rotor is trying to catch the stator rotating field and if the rotor reaches the synchronous speed the torque reaches zero.

 The rotating coming from two parts stator & rotor , there is rotating magnetic field with same current frequency generated by stator , and other magnatic field coming from rotor and according these changing fields produce the above running , depending on frequency .