In English, a mass noun has no plural form, only singular. Contrast this with count nouns, which denote "things". A noun phrase can refer to one or more of these things. A mass noun denotes stuff, or a substance. Stuff, unlike things, is considered to be "divisible". One speaks of removing some stuff from, say, a container. One does not normally speak of a stuff.

Some illustrative examples of English mass nouns:

  • water
  • furniture
  • meat
  • knowledge

Some nouns can have both mass noun and count noun meanings. For example, "laundry" as a mass noun is the stuff you put in the washing machine, i.e. dirty clothes. A "laundry" as a count noun is an establishment which washes clothes, also known as a laundrette. The difference in meaning can be interpreted from whether the item is counted:

"There is laundry on my street." ( must be a mass noun )
"There is a laundry on my street." ( must be a count noun )

This difference is subtle when phrased in the negative:

"There is no laundry on campus."  ( could be either )
"There are no laundries on campus." ( must be a count noun )

Another marker of difference between mass and count nouns is "less" and "fewer":
We have less furniture.
We have fewer chairs.

Many English speakers incorrectly use "less" for both types; in the 1990s several British supermarkets were criticised for their signs above checkouts reading "10 items or less". The correct form is "10 items or fewer": "items" is a count noun, and a mass noun cannot be given a number anyway.

A mass noun can be preceded by a count noun: for example "10 pieces of furniture".

The word "data" is often used as a mass noun, especially by people who work with computers, but this usage is still controversial. In formal writing it retains its original grammatical role as the plural of "datum".

see also English grammar