from
The Free On-line Dictionary of Computing (8 July 2008)
inter-packet gap
<networking> A time delay between successive data {packets}
mandated by the network standard for {protocol} reasons.
In {Ethernet}, the medium has to be "silent" (i.e., no data
transfer) for a few microseconds before a {node} can consider
the network idle and start to transmit. This is necessary for
fairness reasons. The delay time, which approximately equals
the signal propagation time on the cable, allows the "silence"
to reach the far end so that all nodes consider the net idle.
(1995-11-11)