The Collaborative International Dictionary of English v.0.48:

Availability \A*vail`a*bil"i*ty\, n.; pl. Availabilities.
   1. The quality of being available; availableness.
      [1913 Webster]

   Note: The word is sometimes used derogatively in the sense of
         "mere availableness," or capability of success without
         regard to worthiness.
         [1913 Webster]

               He was . . . nominated for his availability.
                                                  --Lowell.
         [1913 Webster]

   2. That which is available.
      [1913 Webster]

WordNet (r) 3.0 (2006):

availability
    n 1: the quality of being at hand when needed [syn: handiness,
         accessibility, availability, availableness] [ant:
         inaccessibility, unavailability]

The Free On-line Dictionary of Computing (19 January 2023):

availability

    The degree to which a system suffers degradation or
   interruption in its service to the customer as a consequence
   of failures of one or more of its parts.

   One of the components of RAS.

   (2000-08-13)