The term broadband refers to the wide bandwidth characteristics of a transmission medium and its ability to transport multiple signals and traffic types simultaneously. The medium can be coax, optical fiber, twisted pair or wireless. In contrast, baseband describes a communication system in which information is transported across a single channel.[1]
Different criteria for "broad" have been applied in different contexts and at different times. It's origin is in physics, acoustics and radio systems engineering, where it had been used with a meaning similar to wideband.[2][3] Later, with the advent of digital telecommunications, the term was mainly used for transmission over multiple channels. Whereas a passband signal is also modulated so that it occupies higher frequencies (compared to a baseband signal which is bound to lowest end of spectrum, see line coding), it's still occupying a single channel. The key difference is that what is typically considered a broadband signal in this sense is a signal that occupies multiple (non-masking, orthogonal) passbands thus allowing for much higher throughput over a single medium, but with additional complexity in the transmitter/receiver circuitry. Finally, the term became popularized through the 1990s as a vague marketing term for Internet access, only barely related to it's original technical meaning.