The Collaborative International Dictionary of English v.0.48:

space bar \space bar\ or space key \space key\ (Mach.,
   Computers)
   A bar or key, in a typewriter, typesetting machine, or other
   keyboard (as a computer keyboard), used to insert a space
   between letters.
   [Webster 1913 Suppl. +PJC]

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

space bar
space key

    (Or "space key") The extra-wide key at the near
   edge of every keyboard that is used to enter a space
   character.

   In some Graphical User Interfaces, the space bar can be used
   to select the current item where the context does not allow
   text entry, e.g. when the input focus is on a push button
   or tick box.

   (2007-01-29)