There are four main types of nouns: proper nouns, common nouns, concrete nouns, and abstract nouns. Proper nouns name specific people, places, or things and are capitalized, while common nouns refer to nonspecific people, places, or things in lowercase. Concrete nouns refer to tangible things that can be seen, touched, heard, tasted, or smelled. Abstract nouns refer to intangible qualities like love, honor, and intelligence. There are also countable and uncountable nouns, collective nouns that group multiple people or things, and compound nouns formed by joining two nouns together.