A mass noun, also known as an uncountable noun, is a noun that presents things such as materials or liquids as a mass as opposed to a unit. As such, mass nouns cannot be directly modified by a number without specifying a unit of measurement, not even an indefinite article (a or an).
Thus, the mass noun "water" can be quantified as "a glass of water" or "3 litres of water", but not normally as "two waters". Everyday exceptions to this use is with coffee, tea and beer, cases where we can use ellipsis to say "Two teas, please" instead of "Two cups of tea, please."
Other examples of mass nouns, with typical units of measurements, include the following:
an advice= some advice; a word of advice; a piece of advice
a bread= some bread; a piece/chunk/slice/loaf of bread
a furniture= an item/a piece of furniture
a lightning= some lightning; a bolt/flash of lightning
a luck= some luck; a stroke/bit of luck
a luggage= some luggage; a piece/an item of luggage
a news= a news item; an item of news; a news article; a piece of news
a research= a piece of research
a rubbish= a load/piece of rubbish
a thunder= some thunder; a clap of thunder
a traffic= a lot of/some traffic
 Differences with other European languages
Some nouns are uncountable in English where they are countable in other European languages. These include:
a new, a news= some/an item of news
informations= an item of/ some information
 Counting the uncountable
Note that when one is speaking about definite, specified uncountable nouns then they can be preceded by a determiner such as "the". For example, "wine" is usually uncountable, but one can say:
- Did you remember to bring the wine to the party?
 Data is/data are
Data comes from a Latin word that means things which are given, and that’s plural. The singular is datum, but most English speaking people don’t know Latin and so not everybody realises that the word was supposed to be plural. Both "data is" and "data are" are now accepted forms.
 Abstract nouns
- BBC Learning English