space bar

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun A bar at the bottom of the keyboard of a computer or typewriter that when pressed down introduces a horizontal space into text, as between words.

from The Century Dictionary.

• noun Same as spacer, 2.

from the GNU version of the Collaborative International Dictionary of English.

• (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.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun computing A key, in the shape of a bar, near the bottom of a keyboard, that generates a space character when pressed

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun the bar-shaped typewriter key that introduces spaces when used