Source : Webster's Revised Unabridged Dictionary (1913)

J \J\ (j[=a]).
   J is the tenth letter of the English alphabet. It is a later
   variant form of the Roman letter I, used to express a
   consonantal sound, that is, originally, the sound of English
   y in yet. The forms J and I have, until a recent time, been
   classed together, and they have been used interchangeably.

   Note: In medical prescriptions j is still used in place of i
         at the end of a number, as a Roman numeral; as, vj,
         xij. J is etymologically most closely related to i, y,
         g; as in jot, iota; jest, gesture; join, jugular, yoke.
         See {I}. J is a compound vocal consonant, nearly
         equivalent in sound to dzh. It is exactly the same as g
         in gem. See Guide to Pronunciation, [sect][sect] 179,
         211, 239.

Source : WordNet®

J
     n 1: a unit of electrical energy equal to the work done when a
          current of one ampere passes through a resistance of one
          ohm for one second [syn: {joule}, {watt second}]
     2: the 10th letter of the Roman alphabet

Source : Free On-Line Dictionary of Computing

J
     
        A derivative and redesign of {APL} with added features and
        control structures.  J is {purely functional} with {lexical
        scope} and more conventional control structures, plus several
        new concepts such as {function rank} and {function array}s.  J
        was designed and developed by Kennneth E. Iverson and Roger
        Hui .  J uses only the {ASCII}
        character set but has a spelling scheme that retains the
        advantages of {APL}'s special alphabet.  J is a conventional
        procedural programming language but can be used as a {purely
        functional} language.
     
        Version 4.1 for {MS-DOS}, Sun, Mac, Archimedes.  Source
        available in C from {Iverson Software}, +1 (416) 925 6096.
     
        Version 6 package from ISI includes an interpreter and
        tutorial.  Ported to {DEC}, {NeXT}, {SGI}, {Sun-3}, {Sun-4},
        {Vax}, {RS/6000}, {MIPS}, {Macintosh}, {Acorn Archimedes},
        {IBM PC}, {Atari}, {3b1}, {Amiga}.
     
        {(ftp://watserv1.waterloo.edu/languages/apl/j)}.
     
        J-mode {GNU Emacs} macros available by
        {(ftp://think.com/pub/j/gmacs/j-interaction-mode.el)}.
     
        ["APL\?", Roger K.W. Hui et al, APL90 Conf Proc, Quote Quad
        20(4):192-200].
     
        (1992-10-31)