Contamination delay

In digital circuits, the contamination delay is the minimum time for a change at the input of a combinational circuit to affect the output. If there is insufficient delay from the output of one flip-flop to the input of the next, the input may change before the hold time has passed. Because the second flip-flop is still unstable, its data would then be "contaminated." Every path from an input to an output can be characterized with a particular contamination delay.

Well-balanced circuits will have similar speeds for all paths through a combinational stage, so the minimum propagation time is close to the maximum. This corresponding maximum time is the propagation delay. The condition of data being contaminated is called a race.

References: 1. http://www.nileshgoel.com/wp-content/uploads/2010/02/timing-note.pdf