In multicore cables, crosstalk denotes interference between adjacent twisted pairs. The electromagnetic field of the signal of one twisted pair induces interference in the adjacent pair.

Crosstalk is a measure of the ability of cabling to reject this interference. It is calculated as the ratio of signals in the transmitting and receiving pairs and is expressed in dB.

Crosstalk can be categorized as Near End Cross Talk, NEXT, or Far End Cross Talk, FEXT.

NEXT denotes crosstalk at the local connection; it is frequency-dependent. FEXT denotes crosstalk at the other end of the cable, minus the original cable attenuation; it is thus length-dependent.