What is the difference between stepper motor and servo motor?

Stepper motor is a special type of motor with more than 2 wires. Each set of wires is connected to a discrete coil, and the power supply that operates these coils allows the motor to move in discrete steps.

These motors are of the common type used in CNC machines with 200 revolutions. This means that for every step the motor takes, it moves 1.8 degrees.

The disadvantage of the stepper is that there is no feedback that the tool head actually has motion. This is called an open-loop system, which is more of a theoretical problem than a practical one, but it's certainly worth mentioning.

Now the servo motor. Usually built into the motor is an optical encoder that lets the motor know if the motion is actually occurring. This creates feedback, which actually guarantees the position of the tool head, and this feedback is fed to the motor, called a closed-loop system.

However, servo motors are very expensive compared to stepper motors and require different expensive boards to run them. Coupled with their higher speed, this makes servo motors a better solution.