Measuring capacitance of Metal-Insulator-Semiconductor (MIS) structure with LCR meter
It's measuring a complex impedance at one or more frequencies and interpreting the measurement as those lumped components. The result is always two numbers at a single frequency, so it should display both (Capacitance and conductance in this case).
If a single-frequency impedance measurement is interpreted as a different circuit, for example parallel RC, the numbers will both change.
The value also gives you an idea of the reliability of the measurement. If the conductance component of the impedance is very small compared to the susceptance of the capacitance then the latter will be more reliable than the former because small phase angle differences will greatly affect the former.