Source : Webster's Revised Unabridged Dictionary (1913)

Focal \Fo"cal\, a. [Cf. F. focal. See {Focus}.]
   Belonging to,or concerning, a focus; as, a focal point.

   {Focal distance, or length, of a lens or mirror} (Opt.), the
      distance of the focus from the surface of the lens or
      mirror, or more exactly, in the case of a lens, from its
      optical center. 

   {Focal distance of a telescope}, the distance of the image of
      an object from the object glass.

Source : WordNet®

focal
     adj 1: having or localized centrally at a focus; "focal point";
            "focal infection"
     2: of or relating to a focus; "focal length"

Source : Free On-Line Dictionary of Computing

FOCAL
     
        1. FOrmula CALculator.
     
        An interactive system written by Rick Merrill of {DEC} in 1969
        for {PDP-5} and {PDP-8}.  It was a descendant of {AID}/{JOSS}.
     
        Versions: FOCAL-69, FOCAL-1971, FOCAL-11 (for {PDP-11} under
        {RT-11}).
     
        (1994-12-21)
     
        2. Forty-One CAlculator Language.
     
        The programming language of the HP-41 calculator line.
     
        (1994-12-21)