What is miller shoot through voltage (aka cross conduction)?
If we look at an inverter leg







simulate this circuit &ndash; Schematic created using CircuitLab

And it is such that the top switch is controlled while the bottom switch has no gate-drive (or gate-source termination). When the top switch is turn-ON/OFF the source of the upper device will be dragged up/down with respect to the load and the supply rail.

Since the top source and the bottom drain are connected, the drain of the bottom switch will also move. 

Now consider the small signal characteristics of such a device 







simulate this circuit

The Cdg capacitance (the miller capacitance) will facilitate charge flow which can charge up the Cgs of the lower device. If this charge is enough to raise the gate voltage to Vth, then the lower FET can potentially start conducting resulting in a shoot-through.

This is why there should always be a gate termination resistor and also a low-impedance gate-drive to absorb such charge flow