In the design of radio broadcast systems, especially television systems, the desired-to-undesired channel ratio (D/U ratio) is a measure of the strength of the broadcast signal for a particular channel compared with the strength of undesired broadcast signals in the same channel (e.g. from other nearby transmitting stations).
See also Signal-to-noise ratio
References http://www.eetimes.com/design/microwave-rf-design/4013009/ATSC-A-74-compliance-and-tuner-design-implications ATSC A/74 compliance and tuner design implications; eetimes.com]