Source : Webster's Revised Unabridged Dictionary (1913)

Em \Em\, n. (Print.)
   The portion of a line formerly occupied by the letter m, then
   a square type, used as a unit by which to measure the amount
   of printed matter on a page; the square of the body of a
   type.

Source : WordNet®

em
     n 1: the square of a body of any size of type [syn: {mutton}, {mut}]
     2: a linear unit (1/6 inch) used in printing [syn: {pica em}, {pica}]

Source : Free On-Line Dictionary of Computing

EM
     
        {End of Medium}