Nouns refer to people, places, things, ideas, or concepts. There are five types of nouns: common, proper, abstract, material, and collective. Common nouns are general names like window or cup. Proper nouns name specific people, places, or things like Mirza Ghalib or Karachi. Abstract nouns refer to ideas or concepts that have no physical form, such as freedom or happiness. Material nouns name materials or substances like cotton or gold. Collective nouns refer to groups of people or things like family or cricket team.