Far End Crosstalk (FEXT) is an electromagnetic interference (EMI), a type of crosstalk, introduced on UTP by close-by wires, usually running in parallel with the FEXT induced wire.

"Far End" refers to the inductance of EMI in the end further from the end being measured on the alternate wire in a pair.

In opposition to this, NEXT (Near End Cross Talk) is the detection of EMI on a wire whose inductance is at the same end as the measurement point. Obviously NEXT is stronger at the other end due to attenuation of the crosstalk signal.

Crosstalk is generally computed as the ratio in voltage between a "test signal" and the induced crosstalk signal in an alternate wire.

Professional computer network cabling must pass TIA/EIA (Telecommunications Industry Association/Electronic Industries Alliance) standards tests, generally TIA/EIA-568-B standard.