Don is correct. It is CNC driven which makes it quite accurate. It is flooded with a dielectric while it is cutting. Sparks jump from the wire or in the case of plunge type, the electrode and erode the material ahead of it. The great part about this process is that there is virtually no residual stress as there is no cutting force. The draw back is that it is slow and expensive.
To a lesser degree is there is a very thin recast layer that is an issue in heavily loaded parts or in high vibration.
Are you sorry that you asked now?