"IDK" is an abbreviation for "I don't know." It is commonly used in informal communication, especially in text messages and online chats. People use "IDK" to express uncertainty or a lack of knowledge about a particular topic or question. This acronym is part of a larger trend of using shorthand in digital communication, which includes other abbreviations like "LOL" (laugh out loud) and "BRB" (be right back). Such shorthand helps convey messages quickly and efficiently, making it easier for users to communicate in fast-paced environments like social media and messaging apps.