Asynchronous I/O is a method of input and output processing that allows a program to continue executing while waiting for data to be read or written. Instead of blocking the program's execution until the operation completes, it uses callbacks or events to notify the program when the operation is finished. This improves efficiency, especially in applications that handle multiple tasks simultaneously. In contrast to synchronous I/O, where operations must complete before moving on, asynchronous I/O enables better resource utilization. It is commonly used in network programming and file handling, allowing applications to remain responsive and perform other tasks while waiting for data from sources like disk drives or network connections.