"Async" refers to asynchronous programming, a method that allows tasks to run independently without blocking the main thread. This means that while one task is waiting for a response, such as fetching data from a server, other tasks can continue executing. This approach improves efficiency and responsiveness in applications, especially in environments like web development. In many programming languages, such as JavaScript and Python, async functions are used to handle operations like API calls or file reading. By using async, developers can write cleaner code that is easier to manage, leading to better performance in applications that require handling multiple tasks simultaneously.