Electrical machines are categorized into two..

There are two types of motor.

AC motor.
DC motor.
There are two types of three phase motor.

Synchronous motor.
12v Motor Asynchronous motor.
The essential difference between asynchronous and synchronous motor , slip presents in asynchronous engine .At running condition slip of an asynchronous electric motor lies from 0 to at least one 1. . In asynchronous electric motor both starting and working torque is required. Asynchronous engine has moderate starting torque . Asynchronous motor is a single fed electric motor.In asynchronous electric motor field is stationary armature rotates .

Three phase synchronous machines have a stationary three phase armature and a wound rotor. They are of two types:

synchronous generator or Alternator: Primary workhorse of the energy generation industry; they are rotated mechanically by a prime mover at synchronous velocity and it creates three phase electricity. Picture of PMA found in cars:
2. Synchronous motor: These are continuous speed three phase machines capable of operating at synchronous quickness. They are mostly found in constant quickness mechanical drives. They are better in comparison to induction motors.
A synchronous machine has derived its name from the concept that the rotor will rotate in synchronicity with the rotating magnetic field.

In other words, for a 2 Pole machine (electric motor) the rotating magnetic field rotates at 3000 rpm; the rotor of synchronous machine also rotates at the same quickness i.electronic. 3000 rpm. This is achieved through special constructional features in manufacturing this types of devices. There is no slip in synchronous machines like normal induction motors.

Normally three phase supply is available commercially and the design is also designed for the same. This is why ‘three phase’ is definitely added with synchronous machine name.