What does 8-bit processor mean?

Could you please clarify for me what exactly is meant by the term "8-bit processor"? I understand it's a type of processor, but I'm curious about the significance of the "8-bit" designation. Specifically, how does an 8-bit processor differ from other types of processors, and what impact does this have on its functionality and capabilities? Is there a limit to the amount of data it can process at once, and how does this limit compare to other processors on the market? Thank you for your help in understanding this concept.