This is often seen by the home inspector as the supply conduit to outside installations, such as air-conditioning compressors.
This AC/BX-type conduit has a PVC outer sheathing to render it watertight, which should be marked "UF" for exterior use. (It is not approved for direct burial, however.)
The picture at the left (courtesy of John Murray) is of ENT conduit supplying an air-conditioning compressor. There is evidence of damage to the outer sheathing, allowing moisture into the cable assembly. This requires replacement of the conduit.