Transistors are 3 terminal semiconductor devices which is able to conduct relatively high power across their two terminals, in response to a significantly low power input at the third terminal.
Transistors are basically of two types: bipolar junction transistor (BJT), and metal–oxide–semiconductor field-effect transistor (MOSFET)
For a BJT, the 3 terminals are designated as base, emitter, collector. A low power signal across base/emitter terminal allows the transistor to switch a comparatively high power load across its collector terminal.
For MOSFETs these are designated as Gate, Source, Drain. A low power signal across Gate/Source terminal allows the transistor to switch a comparatively high power load across its collector terminal.
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