There's actually two wires stuck together. One is for the phone connection and the other which connects to the STB and modem is called coaxial cable or coax. The grade used on most installs has the type name RG6 and is similar to that used for satellite TV to the point that either would be fine for both uses.
http://en.wikipedia.org/wiki/Coax
If you are asking so you can extend one or the other look on eBay for ready made satellite or cable TV extensions.