STP means shielded twisted pair. It usually refers to high-speed data cables, such as Category 5, in a shielded version. The unshielded version, which is much more common, is called UTP, unshielded twisted pairs.
Belden makes shielded twisted pairs. The Category 5 shielded versions are Belden Part # 1589A (2-pair), 1584A (4-pair RJ-45 compatible), 1633A (4-pair), 1591A (2-pair plenum), 1586A (4-pair plenum RJ-45 compatible), and 1646A (4-pair plenum). There are also dual-cable versions available.