On most Sony's it's sub-contrast. There could, however be several of them; main pic, child pic, side-by-side pics. The various inputs may have similar controls but they tend to be labeled brt and con rather than sub-xxx since you can't always adjust them from the menus.
They are usually used to limit the range of the main controls so you can't do as much damage to the picture by mis-adjusting the customer controls and on Sony they can fine tune the "Picture" control since it is a combination brightnes, contrast, and color level adjustment.
ok. so that leads to my next question, which controls do i use when performing calibration? the regular user menu brightness/contrast or the service menu sub.. controls?