curbing

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

• noun The material used to construct a curb.
• noun A row of curbstones; a curb.

from The Century Dictionary.

• noun The act of checking or restraining.
• noun Material prepared for curbstones either roughly worked to dimension, or finished ready to set.

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

• verb Present participle of curb.
• noun A row of curbstones; the material used to construct such a curb
• noun The damage caused to a wheel or tire by curbing (running the wheel or tire into or over a curb).

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

• noun an edge between a sidewalk and a roadway consisting of a line of curbstones (usually forming part of a gutter)