A bootable USB drive is a portable storage device that has been formatted and loaded with software, files, and operating systems necessary to boot up a computer. It allows users to run or install an operating system, such as Windows or Linux, on a computer without using a physical disc drive. Bootable USB drives are often used for system recovery, troubleshooting, and installing software on computers without an operating system. They are easy to create and offer the advantage of being easily swappable and durable compared to optical discs. To create a bootable USB drive, users need to format the drive correctly and copy the required files and operating system onto it.