WordNet (r) 3.0 (2006):

scalability
    n 1: the quality of being scalable

The Free On-line Dictionary of Computing (30 December 2018):

scalability

   How well a solution to some problem will work when the size of
   the problem increases.

   For example, a central server of some kind with ten
   clients may perform adequately but with a thousand clients
   it might fail to meet response time requirements.  In this
   case, the average response time probably scales linearly with
   the number of clients, we say it has a complexity of O(N)
   ("order N") but there are problems with other complexities.
   E.g. if we want N nodes in a network to be able to communicate
   with each other, we could connect each one to a central
   exchange, requiring O(N) wires or we could provide a direct
   connection between each pair, requiring O(N^2) wires (the
   exact number or formula is not usually so important as the
   highest power of N involved).

   (1995-03-29)