Why is it called a "Bipolar" Transistor ?

• The conduction in a bipolar junction transistor takes place due to both, electrons why it is called as a "bipolar" transistor. 

• If the conduction takes place due to only one type of carriers i.e. majority transistor is called as "unipolar" transistor. 

• The example of a unipolar device is the Field Effect Transistor (FET).

Fig. Bipolar Transistor