What is a bipolar transistor, transistor circuits, bipolar junction transistors

Microsemi 2N2222A in Bag. 2N2222A 50 V 800 mA NPN Silicon Switching Transistor - TO-18 (TO-206AA)  

https://www.futureelectronics.com/p/discretes--transistors--bipolar-transistors/2n2222a-microsemi-5054667