In telecommunication, the term duct has the following meanings:
1. In interfacility cabling, a conduit, which may be direct-earth buried or encased in concrete, used to enclose communications or power cables.
Note: For maximum resistance to rodent attack, direct-earth-buried conduit should have an outside diameter equal to or greater than 6 cm (2.25 in.).
2. See atmospheric duct.
Source: from Federal Standard 1037C
