Same as it does for the IS200 and 300 ..It is 'Intermediate Sedan', as the GS is 'Grand Sedan' and the LS is 'Luxury Sedan'.
Tango is right, this is the original definition for the Lexus range
SC stands for Sport Coupé, ES stands for Economy Sedan, GX for Grand Crossover and LX for Luxury Crossover and RX stands for I don't know what :P