A noun is a word (other than a pronoun) used to identify people, places, or things, or to name a particular one of those.
A noun is a word (other than a pronoun) used to identify a class of people, places, or things, or to name a particular member of these classes. In the first case, the term used is "common noun". In the second, the term is "proper noun".
English nouns can broadly be divided into "count nouns" (or "countable nouns") and "mass nouns" (or "non-count" or "uncountable nouns") - though the distinction isn't always clear-cut.
Count nouns have both a singular and a plural form (boat and boats, for example, or woman and women). They can be counted (qualified by numerals), e.g. two boats. Some plurals are regular (boats), a few irregular (women).
Mass nouns are used in the singular only. They don't form a plural (
dirts) and can't be counted. They can be measured or quantified (e.g. a lot of dirt, not much dirt), but are treated as a mass rather than as discrete items.