See mass noun in Webster's New World College Dictionary
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a noun denoting an abstraction or something that is uncountable, and not preceded by a or an: it is typically in a singular construction, but may be singular or plural in form (Ex.: love, girlhood, butter, news)
See mass noun in American Heritage Dictionary 4
noun
A noun, such as sand, oil, or honesty, that denotes a substance or concept indivisible into countable units and is preceded in English indefinite constructions by modifiers such as some or much rather than a or one.