A very short highlight of the differences:
USB - Reformatting the system. New file system. New definition of partition size. New IP. New role (i.e. GW can become management etc.) Nothing is left from the previous installation.
CPUSE Clean - Create a new partition for the new version and install it. The old partition still exists so you can easily revert. Partition sizes are kept as well as files which are not in the "current" partition.
CPUSE Upgrade - Exactly like clean install but at the end of the process a configuration migration is done so the machine expected to stay with same functionality (i.e. you can't change GW to Management etc.)
Blink - Mainly a shortcut to make installation faster in case installation of version + Jumbo is required. The terms clean/upgrade are same as any CPUSE installation (see above) but instead of installing version 80.40, reboot, install jumbo, reboot it can be done in one step (i.e. install 80.40 + jumbo and reboot).