Nouns are naming words that represent people, places, objects, substances, qualities, actions and measures. There are different types of nouns including common nouns, proper nouns, collective nouns, countable nouns, and uncountable nouns. Common nouns refer to classes while proper nouns are specific names that begin with capital letters. Collective nouns refer to groups and pronouns are used to replace nouns. Countable nouns can be counted while uncountable nouns cannot be counted individually.