As part of the Paperwork Reduction Act, the six Registry keys are frequently abbreviated as follows:

HKCR   HKEY_CLASSES_ROOT
HKCC   HKEY_CURRENT_CONFIGURATION
HKCU   HKEY_CURRENT_USER
HKDD   HKEY_DYNAMIC_DATA
HKLM   HKEY_LOCAL_MACHINE
HKU      HKEY_USERS

These abbreviations appear in text descriptions and in INF files that edit the Registry, but not within the Registry itself.