Duct

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