Nouns in English can be either count nouns or noncount nouns. Count nouns refer to distinct individuals or things that can be directly counted: a doctor, an egg, a child; doctors, eggs, children. Noncount nouns refer to masses, collections, or ideas without distinct parts: milk, rice, courage. You cannot count noncount nouns except with a preceding phrase: a glass of milk, three grains of rice, a little courage.

Count nouns usually have singular and plural forms: tree, trees. Noncount nouns usually have only a singular form: grass.

Some nouns can be either count or noncount, depending on their meaning.

When you learn a noun in English, you need to learn whether it is count, noncount, or both. Many dictionaries provide this information.