Nouns are words that name people, places, things, or ideas. There are several types of nouns, including common nouns, which refer to general items like dog or city, and proper nouns, which name specific entities, such as New York or Sarah. Another type is collective nouns, which represent groups, like team or flock. Additionally, abstract nouns refer to concepts or feelings, such as happiness or freedom, while concrete nouns denote physical objects that can be perceived by the senses, like apple or car.