Electrical machines are categorized into two..
Motor.
Generator.
There are two kinds of motor.
AC motor.
DC motor.
There are two kinds of three phase motor.
12v Motor synchronous motor.
Asynchronous motor.
The essential difference between asynchronous and synchronous motor , slip presents in asynchronous electric motor .At running condition slip of an asynchronous engine lies from 0 to 1 1. . In asynchronous electric motor both starting and running torque is necessary. Asynchronous motor has moderate starting torque . Asynchronous motor is usually a single fed motor.In asynchronous electric motor 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: Primary workhorse of the energy generation industry; they are rotated mechanically by a primary mover at synchronous rate and it creates three phase electricity. Picture of PMA used in 
cars:
2. Synchronous motor: They are constant speed three phase devices capable of working at synchronous quickness. They are mostly found in constant velocity mechanical drives. They are better 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 swiftness i.e. 3000 rpm. That is achieved through particular constructional features in manufacturing this types of machines. There is absolutely no slip in synchronous devices like normal induction motors.
Normally three phase supply is available commercially and the design is also designed for the same. That is why ‘three phase’ is usually added with synchronous machine name.