This command toggles the visibility of undiscovered regions on the local map which are usually covered by 'Fog of War'. Only the local map is affected by this command - the world map, etc are left unchanged.
If Fog of War is enabled, this command will disable it, making all regions on the local map visible. If Fog of War is disabled, running this command will re-enable it.
ToggleFogOfWar is simply a longer version (alias) of the TFOW command - it has the exact same function.