2N2222 is a typical
NPN positive contactor transistor (BJT) used in general purpose low power amplification or switching applications. Designed for low current, low power and medium voltage, it can operate at moderate high speed. It was originally made of a TO-18 metal can as shown in the picture.
2N2222 is considered a very common transistor and is used as an example of NPN transistors.
It is often used as a small signal transistor and remains a small general-purpose transistor of sustained popularity.