In
linguistics, a
count noun (also
countable noun) is a noun that can be modified by a
numeral and that occurs in both
singular and
plural forms, and that co-occurs with quantificational
determiners like
every,
each,
several, etc. A
mass noun has none of these properties. It can't be modified by a numeral, occur in singular/plural, or co-occur with quantificational determiners.