What is MUX in transmission?

Could you please elaborate on what MUX stands for in the context of transmission? I'm curious to understand how it is used and its significance in the field of telecommunications. Is MUX a hardware component, a software tool, or perhaps a specific protocol? How does it help in the process of transmitting data and what are some of its key benefits or advantages over other methods? Thank you for your time and consideration in addressing this question.