I'm trying to make a reservation for the St. Regis in New York using points. I get to a screen that lets me select my room and each selection shows:

Room Type:
Room Description:
Bed Type:
Feature:

The last three are the same for all four selections:

Room Description: SPG AWARD ROOM
Bed Type: KING
Feature: SMOKING

But the Type is different for each:

Room Type: C
Room Type: F
Room Type: J
Room Type: X

Does anyone know what these codes mean?