In most modern metal shops, you'll find both a lathe and a vertical mill. Both machines function by removing material from a block of metal--the "workpiece." The key difference between the two is how the workpiece is handled. On a lathe, the workpiece rotates, and is cut away by a knife tool. (Typical products of lathe work are "turned parts" such as spindles, bearings, screws, washers, and circular blanks for gears.)
On a milling machine, it's...