What term describes unwanted signal coupling from one pair of a 4-pair cable to another?

The correct term that describes unwanted signal coupling from one pair of a 4-pair cable to another is crosstalk. Crosstalk refers to the phenomenon where a signal transmitted on one pair of wires in a cable interferes with the signal on another pair. This interference can arise due to capacitive, inductive, or electromagnetic coupling between the pairs, which can negatively impact the performance of the communication system.

In the context of twisted pair cabling typically used in networking, proper cable design and installation practices are crucial to minimizing crosstalk. This is why terms such as "FEXT" (far-end crosstalk) and "NEXT" (near-end crosstalk) are also important but specifically relate to the nature of these crosstalk effects at different points along the cable. "AXT" (alien crosstalk) describes interference from external cables, which can also occur.

Understanding crosstalk and its effects is essential for ensuring high-quality transmission in network installations, making it a key concept in the field of data communications and cabling.