Countable nouns (or count nouns) are those that refer to something that can be counted. They have both singular and plural forms (e.g. cat/cats; woman/women; country/countries). In the singular, they can be preceded by a or an.
They may be the names for abstract ideas or qualities or for physical objects that are too small or too amorphous to be counted (liquids, powders, gases, etc.). Uncountable nouns are used with a singular verb. They usually do not have a plural form.