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]

WordNet (r) 3.0 (2006):

space bar
    n 1: the bar-shaped typewriter key that introduces spaces when
         used

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

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, pressing the space bar
   selects 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)