signalling event

Short definition from Wiktionary

Noun

1. 1
   A transmitter encodes data by producing a signal which is a continuous stream of signalling events each which has sufficient information for the receiver to recover the original data. Just like a quantum leap is the smallest measurable leap, a signalling event is the smallest possible amount of signal that the receiver needs to recover the original data without error.
2. 2
   A change of the state of a communication channel, each state representing a symbol that is to be transmitted.