UPX is a file compression tool that reduces the size of executable files, such as those used in software applications. It works by applying advanced algorithms to compress the binary data without affecting the program's functionality. This makes it easier to distribute software and saves storage space. The primary benefit of using UPX is that it can significantly decrease the file size, which is especially useful for developers and users who need to share applications over the internet. Additionally, UPX supports various executable formats, making it versatile for different operating systems and platforms.