EDM stands for Electrical Discharge Machining; in everyday language it is also known as spark erosion. It is a manufacturing method that uses the power of sparks to shape conductive metals precisely, no matter how hard they are.
Let's explain it simply
A “controlled” spark squeezed between two metal parts causes a number of small craters to appear.
Craters
The micro-craters on the part are formed by the local fusing of the material caused by the very high temperatures produced by the sparks.