[DanielG]

A master clone is a direct copy from the master tape (DAT, miniDV) that has been performed digitally and with no quality loss.

For example, if you filmed a show on your miniDV camcorder and then used Firewire to copy the tape onto another miniDV tape (or Digital8 tape) then the copy will be a master clone.

Theoretically, you could keep on copying subsequent copies and they would all be clones of the master.

You can't have a master clone if either the source or the copy is in an analog form such as VHS, S-Video, video8, Hi-8, audio cassette etc.
ie. Master miniDV tape copied to VHS.