Hint:In order to answer the given question, to know about the emitter of the transistor, we should go through the whole concept of the transistor and what the use or existence of the emitter in the transistor is.
Complete answer: The emitter of the transistor is heavily doped, and its job is to emit and inject electrons for NPN (or holes for PNP) into the base. The word Transistor is formed from two words, one is “Transfer” and other is “Varistor”. This means that a transistor is a system that moves resistance from one circuit channel to another. It's a three-terminal current-controlled system that can be used as a switch or an amplifier when given a low signal voltage. It's one of the most popular kinds of active devices.
As we know, an emitter is one of the terminals of the transistor. In comparison to the base and collector, the emitter terminal is the most heavily doped field. Since the emitter's job is to supply charge carriers to the collector through the foundation, this is the case. The emitter is larger than the base but smaller than the collector.
Note: The main feature of this circuit, as its name suggests, is that the emitter circuit is shared by both the input and output. Both NPN and PNP transistors will benefit from the common emitter configuration. However, since NPN transistors are more widely used, the NPN variety is more frequently used.