Source : Webster's Revised Unabridged Dictionary (1913)

Scalar \Sca"lar\, n. (Math.)
   In the quaternion analysis, a quantity that has magnitude,
   but not direction; -- distinguished from a vector, which has
   both magnitude and direction.

Source : WordNet®

scalar
     adj : of or relating to a directionless magnitude; "scalar
           implicatures"

scalar
     n : a variable quantity that cannot be resolved into components

Source : Free On-Line Dictionary of Computing

scalar
     
        1.  A single number, as opposed to a {vector} or
        {matrix} of numbers.  Thus, for example, "scalar
        multiplication" refers to the operation of multiplying one
        number (one scalar) by another and is used to contrast this
        with "matrix multiplication" etc.
     
        2.  In a {parallel processor} or {vector
        processor}, the "scalar processor" handles all the sequential
        operations - those which cannot be parallelised or vectorised.
     
        See also {superscalar}.
     
        3.  Any data type that stores a single value
        (e.g. a number or {Boolean}), as opposed to an {aggregate}
        data type that has many elements.  A {string} is regarded as a
        scalar in some languages (e.g. {Perl}) and a vector of
        {characters} in others (e.g. {C}).
     
        (2002-06-12)