I am not an electrician. I did study electrical engineering but not power.
However, what is generally going on with a flicker is the surge current of the device is very high. This is the initial current anything draws when you turn it on. For example, a heating element in an iron, looks like a dead short when it is turned on. Huge current draw. As the temperature goes up, so does the resistance, which causes the current to fall. They do this to get them to heat up more quickly.
And house wiring is not perfect. It is quite inductive. Inductors resist the change of current flowing in them. So, one end of the inductor is shorted to ground with the heater, that draws all of the electrons out of the vacinity and the voltage drops locally. Eventually this low voltage, which causes the lights to flicker, makes its way to the main input from the power line. The power line is much less inductive and resistive and is able to recharge the house quickly. So the lights return to normal.
You should see it here when my electric furnace kicks on. It takes about 30 amps off of both phases. But doesn't hurt anything.
It may be aggravated if you have 14 gauge wiring or aluminum wires. They are more resistive.