R - Can be reloaded in game with .reload without restart.
T - These tables are maintained by the core team. Any table that is marked with a T should have the data in the Trinity Core repo. If it is NOT marked with a T then the data must go into TDB. (Deprecated)
EXTERNAL - These tables hold external data and are not maintained by the TrinityCore development team.
I - Internal table used by Trinity during runtime.