_FIX_CONTROL is a special hidden dynamic parameter introduced in 10.2.0.2 which can be used to enable or disable certain bug fixes. This is typically used in the optimizer area to allow specific fixes to be turned on or off as some fixes can have a significant effect on execution plans.
The VALUE column shows the current state of the bug fix, where 1=ON and 0=OFF.
They can be set on system level or on session level.