'unrestricted-band' originates from the combination of 'unrestricted,' meaning 'not limited or controlled,' and 'band,' referring to a range of frequencies.

The term 'band' in telecommunications has been used since the early 20th century, while 'unrestricted' has been used in various contexts to denote lack of limitations.

Initially, 'band' referred to a range of frequencies, and 'unrestricted' meant without limitations. The combined term 'unrestricted-band' has maintained this meaning in modern usage.