The word ‘girl’ is a common noun.
Common nouns are general names for a person, place, or thing. They do not refer to a specific individual and can be used to describe any member of a category. In this case, ‘girl’ refers to any female child or young woman, without identifying a particular person.
On the other hand, a proper noun would refer to a specific name, such as ‘Sarah’ or ‘Emily.’ Proper nouns are always capitalized, while common nouns like ‘girl’ are not unless they begin a sentence.