number line

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

• noun A line that graphically expresses the real numbers as a series of points distributed about a point arbitrarily designated as zero and in which the magnitude of each number is represented by the distance of the corresponding point from zero.

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

• noun mathematics A line that graphically represents the real numbers as a series of points whose distance from an origin is proportional to their value