The key opens only one padlock.
Each padlock has its own key.
All keys are the same and open all padlocks within in a group.
A Master Key can open all padlocks across several groups (KD and or KA).
A Grand Master Key sits at the highest level of access and opens all padlocks, including: groups of Keyed Different Padlocks groups of Keyed Different Padlocks with a Master Key groups of Keyed Alike padlocks with a Master Key mixed Groups of Keyed Alike, Keyed Different and Master Keyed Padlocks