Source : Webster's Revised Unabridged Dictionary (1913)

Alt \Alt\, a. & n. [See {Alto}.] (Mus.)
   The higher part of the scale. See {Alto}.

   {To be in alt}, to be in an exalted state of mind.

Source : WordNet®

ALT
     n : angular distance above the horizon (especially of a
         celestial object) [syn: {elevation}, {EL}, {altitude}]

Source : Free On-Line Dictionary of Computing

alt
     
         /awlt/ 1. The alt {modifier key} on many
        {keyboards}, including the {IBM PC}.  On some keyboards and
        {operating systems}, (but not the IBM PC) the alt key sets bit
        7 of the character generated.
     
        See {bucky bits}.
     
        2. The "{clover}" or "Command" key on a {Macintosh}; use of
        this term usually reveals that the speaker hacked PCs before
        coming to the Mac (see also {feature key}).  Some Mac hackers,
        confusingly, reserve "alt" for the Option key (and it is so
        labelled on some Mac II keyboards).
     
        3. (Obsolete {PDP-10}; often "ALT") An alternate name for the
        {ASCII} ESC character (Escape, ASCII 27), after the keycap
        labelling on some older {terminals}; also "altmode"
        (/awlt'mohd/).  This character was almost never pronounced
        "escape" on an {ITS} system, in {TECO} or under {TOPS-10},
        always alt, as in "Type alt alt to end a TECO command" or
        "alt-U onto the system" (for "log onto the [ITS] system").
        This usage probably arose because alt is easier to say.
     
        4.  One of the {Usenet} {newsgroup} {hierarchies}.
        It was founded by {John Gilmore} and {Brian Reid}.  The alt
        hierarchy is special in that anyone can create new groups here
        without going though the normal voting proceduers, hence the
        regular appearence of new groups with names such as
        "alt.swedish.chef.bork.bork.bork".
     
        [{Jargon File}]
     
        (1997-04-12)