HKey steht für Hive Key. (engl. Haufen, Schwarm)
HKey (HiveKey)
This is a part of the Windows registry hive. The hive contains several different pieves or keys that are somehow associated. Basically a HKEY can be seen as a directory within the registry.
Some examples are:
HKEY_CLASSES_ROOT, HKEY-CURRENT_USER, etc.