1. Two insulated copper wires twisted around each other to reduce induction (thus interference) from one wire to the other. The twists, or lays, are varied in length to reduce the potential for signal interference between pairs. Several sets of twisted-pair wires may be enclosed in a single cable. In cables greater than 25 pairs, the twisted pairs are grouped and bound together in a common cable sheath. Twisted pair cable is the most common type of transmission media. It is the normal cabling from a central office to your home or office, or from your PBX to Your office phone. Twisted pair wiring comes in various thicknesses, As a general rule, the thicker the cable is, the better the quality of the conversation and the longer cable can be and still get acceptable conversation quality. However, the thicker it is, the more it costs.
2. Low-speed tranmission cable comprising two or more pairs of insulated wires twisted together at six twists per inch; may be shielded (STP) or unshielded (UTP). The twisting provides a measure of protection from electromagnetic and radio-frequency interference. Commonly used in telephony applications and increasingly used in networks.