Proper nouns are specific names used to identify particular people, places, or organizations. They always begin with a capital letter. For example, in the sentence "I visited Paris last summer," the word Paris is a proper noun because it refers to a specific city. Proper nouns can also include names of individuals, such as Albert Einstein, or brands, like Coca-Cola. Unlike common nouns, which refer to general items or concepts, proper nouns provide unique identification. For instance, "dog" is a common noun, while "Fido" is a proper noun when used as a specific dog's name.