In telecommunication, the term intersymbol interference has the following meanings:

1. In a digital transmission system, distortion of the received signal, which distortion is manifested in the temporal spreading and consequent overlap of individual pulses to the degree that the receiver cannot reliably distinguish between changes of state, i.e. , between individual signal elements.

Note 1: At a certain threshold, intersymbol interference will compromise the integrity of the received data.

Note 2: Intersymbol interference attributable to the statistical nature of quantum mechanisms sets the fundamental limit to receiver sensitivity.

Note 3: Intersymbol interference may be measured by eye patterns.

2. Extraneous energy from the signal in one or more keying intervals that interferes with the reception of the signal in another keying interval.

3. The disturbance caused by extraneous energy from the signal in one or more keying intervals that interferes with the reception of the signal in another keying interval.

Source: from Federal Standard 1037C and from MIL-STD-188