In Korean, "은/는" are particles used to indicate the topic of a sentence. "은" is used after a consonant, while "는" follows a vowel. These particles help to emphasize or contrast the topic, making it clear what the sentence is about. For example, in the sentence "사과는 맛있다" (The apple is delicious), "사과" (apple) is the topic. Using "은/는" can also help differentiate between general statements and specific information. For instance, if you say "고양이는 귀엽다" (Cats are cute), it implies a general statement about all cats. This makes "은/는" essential for effective communication in Korean.