What is a power MOSFET?
We all know how to use a diode to implement a switch. But we can only switch with it, not gradually control the signal flow. Furthermore, a diode acts as a switch depending on the direction of signal flow; we can't program it to pass or block a signal. For such applications involving either "flow control" or programmable on/off switching we need a 3-terminal deviceand Bardeen & Brattain heard us and "invented" (almost by accident, like many other great discoveries!) the bipolar transistor. Structurally it is implemented with only two junctions back-to-back (no big deal; we were probably making common cathodes - same structure - long before Bardeen). But functionally it is a totally different device which acts like a "faucet" controlling the flow of emitter current - and the "hand" manipulating the faucet is the base current. A bipolar transistor is therefore a current controlled device.
The Field Effect Transistor (FET), although structurally different, provides the same "faucet" function. The difference: the FET is voltage controlled; one doesn't need base current but voltage to exercise flow control. The bipolar transistor was born in 1947; the FET (at least the concept) came soon after, in 1948 from another pair of illustrious parents: Shockley and Pearson. The terminals are called DRAIN instead of COLLECTOR, GATE instead of BASE and SOURCE instead of EMITTER to differentiate it from his older bipolar "cousin". The FET comes in two major variants, optimized for different types of applications: the JFET (junction FET) used in small-signal processing and the MOSFET (metal-oxide semiconductor FET) mainly used in linear or switching power applications.