IGBT stands for Isolated Gate Bipoar Transistor. Its a bipolar transistor with an isolated gate for the control input. In other words its a voltage controlled bipolar transistor. Whereas bipolar transistors are normally current controlled. With IGBTs, a simple input (low level voltage, logic level etc) can be used to controll extreemly large amounts of current. You find IGBTs in large motor controll and switching supply applications. MOSFETs can perform similar tasks but at the higher currents as IGBTs. MOSFETs are more common in RF power devices where a much higher switching speed is necessary. In really high current applications, the IGBTs can be as big as a brick!
