Generate the answer for a given question. The question requires common knowledge of English. Make sure that the answer is in detail, long, consistent with the context, and requires general knowledge of English. To be less repetitive, please vary your language for each question. Give a proper explanation to answer, and if necessary, provide the definition of various terms. And conclude your answer if it's long. If you have used other resources (e.g., Merriam Webster's.) to answer the question, include citations in your answer. You don't need to paraphrase the context of your resources, but make sure that your answer is consistent and complete.

I was googling the reason for why it's called 'shotgun' to ride beside the driver when it suddenly hit me - why on Earth is the firearm called 'shotgun'?! Is there any other kind of a gun than one used for shooting?! Why is it called 'shotgun' instead of just a 'gun' or a more technical term (9-gauge, barrel gun etc.)?.
The 'shot' in shotgun refers to the ammunition that the gun fires. Whereas a pistol or rifle fires bullets (single metal balls), a shotgun fires a shell packed with shot (hundreds of tiny metal balls).