A BufferedOutputStream is a Java class that enhances the performance of output streams by using a buffer. When data is written to a stream, it is first stored in a temporary memory area (the buffer) before being sent to the underlying output stream. This reduces the number of I/O operations, making data writing more efficient, especially when dealing with large amounts of data. The BufferedOutputStream is often used in conjunction with other output streams, such as FileOutputStream or OutputStreamWriter. By wrapping these streams in a BufferedOutputStream, developers can improve the speed of data writing while minimizing the overhead associated with frequent disk access.