A machinist is a person whose job is to run a machine, most often in a factory. Though actually, it is a little more skilled than “anyone who presses a button.” A machinist usually works with machine tools — lathes, mills, grinders — cutting and shaping metal (sometimes plastic) so a part comes out the exact size the drawing asks for. They set the machine, watch the cut, and check the piece. In everyday factory talk people may use it more loosely for someone on a line; in the trade it still means the person who can make the metal do what the plan says. It is a job word, fairly neutral, a little older than operator or CNC technician, but still used with respect. It is not the same as mechanic: a mechanic mends a machine that is already built; a machinist makes or finishes the parts.