Single License unlocks AddressBook Cleaner for one user. And you are only permitted to have one full version installed on your computer.
Pair Pack is for users who want to use the applicaton on two computers, for example one for office the other for home or desktop computer and laptop.
Family Pack includes 4 unique registration codes. Each can unlock one copy of the software application on your family computers.
Site License contains 10 unique registration codes, it is for users who want to use the applicaton on more than 10 computers, like companies.