"It" is a pronoun used in the English language to refer to a subject that is either unknown, unspecified, or previously mentioned. It can represent objects, animals, or ideas, making it a versatile word in communication. For example, in the sentence "The book is on the table; it is interesting," "it" refers to the book. In addition to being a subject pronoun, "it" can also function as an anticipatory subject in sentences. For instance, in "It is raining," "it" does not refer to a specific noun but instead introduces the situation. This usage helps convey information without needing to specify a subject directly.