Electrical machines are categorized into two..

There are two kinds of motor.

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

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

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

synchronous generator or Alternator: Main workhorse of the energy 12v Motor generation industry; they are rotated mechanically by a primary mover at synchronous acceleration and it creates three phase electricity. Picture of PMA used in cars:
2. Synchronous motor: These are constant speed three phase machines capable of running at synchronous acceleration. They are mostly found in constant quickness mechanical drives. They are more efficient compared 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 acceleration i.e. 3000 rpm. This is achieved through special constructional features in manufacturing this types of devices. There is absolutely no slip in synchronous devices like normal induction motors.

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