IDK is an abbreviation for I don't know, used in social media and text messages. Learn more about its meaning, usage and translations in different languages. The meaning of “IDK” is “I don’t know.” It is a common abbreviation used in texting and online communication. This phrase is helpful when you need to quickly express uncertainty or admit that you do not have the answer to a question. It’s widely recognized and saves time, making it perfect for fast-paced digital conversations. Using “IDK” is informal, so it’s best used in casual chats rather than professional or official communications. You can use idk the same way you use the phrase I don’t know. In informal writing, and especially in text messages, the rules of capitalization are lax at best, so you can choose how you want to treat idk. What does the abbreviation IDK stand for? Meaning: I don't know. How to use IDK in a sentence.