In telecommunication, the term wideband modem has the following meanings:

1. A modem whose modulated output signal can have an essential frequency spectrum that is broader than that which can be wholly contained within, and faithfully transmitted through, a voice channel with a nominal 4-kHz bandwidth.

2. A modem whose bandwidth capability is greater than that of a narrowband modem.

Source: from Federal Standard 1037C and from MIL-STD-188