Most of us have been taught that a noun is a word that refers to a person, place, or thing. While this is true, it is helpful to think of thing as a broad category; a thing does not have to be something that you can hold in your hand (a mountain, a place, and a feeling can all be things). Here are some examples of nouns:
Toni Morrison is my favorite writer. (Toni Morrison is a noun and a person)
I do not want to go to Seattle. (Seattle is a noun and a place)
I will eat that marshmallow. (Marshmallow is a noun and a thing)
Eating the marshmallow gave me happiness. (Happiness is a noun and a thing).
Nouns can also refer to an animal (moose), a quality (softness), an idea (zero), or an action (as in “her singing was beautiful”). Nouns can name someone or something generally (dog, seashore, friend) or specifically (Great Pyrenees, Cape Cod, Sally). And although most nouns consist of a single word, some do not: school bus, Italian dressing, and chuck-will’s-widow are all nouns.
Nouns can be singular ('one sandwich') or plural ('two sandwiches'), although some nouns take the same form regardless ('one sheep,' 'two sheep'). Nouns can also refer to concepts (information) that cannot be counted and singular entities (Neptune) that cannot be pluralized.
Sentences can have one noun (“Theo ran quickly.”) or more than one (“Theo ran quickly across the field.”) but some sentences don’t have any (“Run, quickly!”).
Other parts of speech:
What is an adjective?
What is an adverb?
What is a preposition?
What is a verb?
Other articles you may be interested in:
Adjectives that look like nouns
Nouns that look like adjectives