Ion engines are an "electric propulsion system". They make use of the fact that a current flowing across a magnetic field creates an electric field directed sideways to the current.
This is used to accelerate a beam of ions (charged atoms) of xenon away from the spacecraft, thereby providing thrust.
They say the IONs being pushed out the engine are travelling so fast they act as a sort of atomic sandblaster, knocking atoms off the surface of anything they hit.
The techonology will one day be used to propel spacecraft to distant planets. Now that's pretty cool!