electrical discharge machining (EDM) - metalworking operation utilizing spark erosion for very precise shaping of the metal workpiece. The workpiece (anode) and electrical tool (electrode) are placed in a bath of dielectric fluid and brought closer together until the voltage overcomes the insulating effect of the fluid, causing a spark between the tool and workpiece. Consecutive discharges produce a series of micro-craters on the workpiece until the desired shape is achieved. See electrical discharge machining fluid, metalworking lubricant.