contour line

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

• noun A line on a map that joins points of equal elevation.

from The Century Dictionary.

• noun In surveying, a line joining points of equal elevation on a surface; a line or level carried along the surface of a country or district at a uniform height above the sea-level.

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

• noun geography A line on a map through points of equal elevation, often height above sea level.

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

• noun a line drawn on a map connecting points of equal height