Nouns are words that name people, places, things, or ideas. There are two main types of nouns: common nouns, which name any person, place or thing; and proper nouns, which begin with a capital letter and name a specific person, place, or thing. Nouns can also be classified as concrete if they name something tangible, or abstract if they name an intangible concept. There are several other types of nouns including compound nouns formed from multiple words, and collective nouns that name a group. Nouns function as subjects and objects in sentences.