'space bar' definitions:

Definition of 'space bar'

(from WordNet)
noun
The bar-shaped typewriter key that introduces spaces when used

Definition of 'space bar'

From: GCIDE
  • 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]