A mass noun, non-count noun or uncountable noun is a noun that is treated as a single unit regardless of quantity rather than something that contains subsets. They are distinguished from count nouns.
Different languages have different ways of distinguishing mass nouns from count nouns. In both English and Spanish a mass noun cannot be used with a numeral without also specifying a unit of measurement, and in English they cannot be used together with the indefinite article a/an, and they cannot be used in the plural.
Some nouns have both a mass meaning and a count meaning.