dd – strictly works with block systems, not filesystems. It takes an input file (if), an output file(of) and block size as arguments. It copies everything block for block from one block device / file to another. That’s why you can use dd to create a bootable USB. it takes the if of an .iso and an of of /dev/sdb (a usb drive perhaps) and copies it straight over. Requires sudo in many cases because we’re dealing directly with devices (/dev/sd*).