Multi-threading is a programming technique that allows a single program to perform multiple tasks simultaneously. By dividing a program into smaller parts called threads, each thread can run independently, making better use of the computer's resources. This can lead to improved performance, especially in applications that require heavy processing or need to handle multiple tasks at once. In a multi-threaded application, threads can share data and communicate with each other, which helps in completing tasks more efficiently. However, managing these threads can be complex, as developers must ensure that they do not interfere with each other, leading to potential errors or slowdowns.