"이 (This)" is a demonstrative pronoun in the Korean language used to indicate something that is close to the speaker. It helps specify a particular object or person that is nearby or being referred to in conversation. For example, when pointing to a book, one might say "이 책" which means "this book." In addition to its use as a pronoun, "이" can also function as a particle in sentences. It is often used to mark the subject of a sentence when the subject is a noun that ends in a consonant. For instance, "이 사람은 학생이에요" translates to "This person is a student."