Miller Plateau
The region where the gate voltage stays almost constant for a while while a MOSFET is being switched. During this period all of the drive current goes into discharging the drain–gate capacitance and the drain voltage falls; the greater part of the switching loss is produced in exactly this interval.
When you feed current into the gate, the voltage first rises up to the threshold value, then runs flat for a while, and afterwards climbs up to the driver supply value. The flat region in the middle is the Miller plateau. Here the gate voltage is constant because the current supplied is flowing into the feedback capacitance that follows the fast change in the drain voltage.
The importance of this region is this: the drain voltage changes exactly at this time, that is, current and voltage are both non-zero at the same moment. Most of the switching loss is produced here. The duration of the plateau is determined by the ratio of the feedback charge to the drive current; the stronger the driver, the shorter the plateau and the smaller the loss.
This also explains why the gate resistor is so influential: the resistor directly limits the current flowing during the plateau. The result you can observe in the field is this: a power stage that heats up far more than expected at the same current is most often heating up not because of excess current but because it stays too long in the transition region.
The context in which this term is used: DC Motor Driver Selection Guide