Degradation

1. The deterioration in quality, level, or standard of performance of a functional unit.

2. In communications, a condition in which one or more of the required performance parameters fall outside predetermined limits, resulting in a lower quality of service.

Note: Degradation is usually categorized as either "graceful" or "catastrophic."

Source: from Federal Standard 1037C

There are several forms and causes of degradation in electric signals, both in the time domain and in the physical domain: runt pulse, spike, jitter, wander, swim, drift, glitch, ringing, crosstalk, antenna effect, phase noise