Sets the value of a CVar to its coded default value as returned from GetCVarDefault()
- Returns all CVars back to their default values. Note that a message will appear "You do not have permission to perform that function" but that is normal behavior because of some protected cvars.
- Sets the maxFPS CVar back to its default value (100).
/console cvar_default maxFPS
- Resetting the WoW User Interface by deleting the game client or WTF folder does not completely reset your CVars.
- This is different from the "Defaults" button which only resets the CVars set from the interface options. 
- AdvancedInterfaceOptions - Includes a CVar browser that can show any non-default values
- Blizzard Support article: Resetting the WoW User Interface under "Advanced Troubleshooting"