IGBT = Insulated Gate Bipolar Transistor.

A bipolar transistor is a sandwich of three layers of an element from column 4 of the periodic table, usually silicon. If you inject or suck out electrons from the middle layer (depending on type) you cause a current to flow between the outside layers. In a power transistor it takes a lot of power to drive it but it switches on hard (low losses) and with the proper drive circuitry can be fast.

Insulated Gate Field Effect Transistors are switched on by a metal contact insulated by a layer of quartz. They take very little power to drive but they have a relatively high resistance and are impractical for very high power applications. You would have to use lots in parallel. They are the transistors in computer chips.

So somebody combined the two, a bipolar transistor with an insulated gate. It turns on hard and it takes little power to drive. The main disadvantage is that it is slower as you can't turn it off fast by removing carriers (electrons) via the gate - remember, it is insulated.

But the speed has advanced to the point that they are the go to technology for controlling variable speed motors.

And that is probably more than you wanted to know.

Trams used to use ignitrons to do the same job starting in the 1930's. An ignitron is a tube with a pool of mercury and an electrode that starts an arc to switch it on.