The particle "을" is a grammatical marker in the Korean language used to indicate the object of a verb. It is attached to nouns that end in a consonant. For example, in the sentence "사과를 먹다" (to eat an apple), "사과" (apple) is the object, and "을" is added to show this relationship. When a noun ends in a vowel, the particle "를" is used instead. For instance, in "책을 읽다" (to read a book), "책" (book) takes "을" because it ends in a consonant. Understanding how to use "을" and "를" is essential for constructing clear sentences in Korean.