“dd is a command-line utility for Unix and Unix-like operating systems whose primary purpose is to convert and copy files” (Wikipedia). It is very powerful and runs on a low level, so users must be extremely careful with the commands they use.
dd can make perfect byte-for-byte images of just about anything digital, and is most commonly used to copy entire drives. It is, therefore, one of the options offered by MX Live-USB Maker.
The command is very straightforward:
# dd if=/dev/sda of=/dev/sdb
if = the source drive you’re taking the data from
of = the file or location where you want your data saved
Many other uses can be found in the resources linked below.