Shielded
twisted pair. Traditionally, this kind of
network cable has a shield of
braided copper surrounding the signal cables.
There is also a kind of twisted pair cable that has a metal foil instead of a braided shield - this type, whilst actually being shielded, is commonly referred to as Foiled Twisted Pair, abbreviated FTP.
Whichever type of shielding you are using - remember to connect the shield to the metal on your shielded RJ45 connector, or it will be of little use.