A USB Drive is the only device or component that can be used as a boot device. FDISK refers to the command line tool and a Floppy Disk.
USB drive may refer to:
A USB flash drive or "thumb drive", a USB-connected computer storage using semiconductor non-volatile random-access memory
A USB external drive, a hard drive fitted with a USB interface
Secure Digital, a non-volatile memory card format
CompactFlash, a flash memory mass storage device
Memory Stick, a removable flash memory card …