1. The excursion of a radio wave from the Earth to the ionosphere and back to the Earth.
Note: The number of hops indicates the number of reflections from the ionosphere.
2. A waveform transmitted for the duration of each relocation of the carrier frequency of a frequency-hopped system.
3. To modify a modulated waveform with constant center frequency so that it frequency hops.
Source: from Federal Standard 1037C and from MIL-STD-188
4. One step, from one router to the next, of the path of a datagram on internet. The whole journey from source to destination may take for example 10 hops. See also Internet Protocol.