X_LEXICON_USAGE is a fixed lexicon with the following values:

Saved
Value
Displayed Value
CG Pre-loaded
The system created and controls the information and it will be overwritten with every update.
OB Obsolete
The information is no longer used.
PD Development
The information is in development.
UD User Defined
The user created and controls the information and it will not be overwritten when you receive a software update.