Nouns are words that refer to people, places, things, or ideas. There are different types of nouns including common nouns, which are general names, and proper nouns, which are specific names that are usually capitalized. Nouns can also be concrete and refer to tangible objects, or abstract and refer to intangible concepts. Additionally, nouns can be countable, referring to items that can be counted individually, or uncountable (mass) nouns, referring to items that cannot be easily counted individually. Collective nouns refer to groups of people, animals, or things. Understanding nouns is important for constructing sentences and expressing ideas clearly.