LiveUSB means a usb stick from which you can boot linux temporarily (in case of Ubuntu LiveUSB, the option says something like “try Ubuntu before installing”) and which also provides you an option to install/reinstall the OS.
You can boot from a USB like that and still access and manipulate files on your SSD/HDD.
No hard requirement for it to be the same distro that you have installed, just convenient in case you want to reinstall.