mass noun

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

• noun A noun, such as furniture, water, or honesty, that cannot be modified by the indefinite article, does not occur in the plural, and is often preceded by modifiers such as some or much or by a phrase containing a unit of measurement. Some nouns can function both as mass nouns (There are sixty boxes of tile in the warehouse) and as count nouns (We had to cut a tile in half to fit the end of the row).

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

• noun A noun that normally cannot be counted.

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

• noun a noun that does not form plurals