Nouns are words that name people, places, things, or ideas. There are several types of nouns including concrete nouns, which name tangible things that can be sensed, and abstract nouns, which name intangible concepts. Nouns can also be compound words made of multiple words or collective nouns that refer to groups. Nouns function in sentences as subjects and objects, answering the questions of who or what. New nouns can be created over time through invention or borrowing from other languages.