A measure of the extent to which electromagnetic waves are in step with one another. On an astrophysical scale, maser sources are the most notable emitters of coherent radiation.
Statistics
A term used to describe the resemblance between the fluctuations displayed by two time series; an analogue of correlation.
Geology and Earth Sciences
Two wave trains which are in phase. Coherence is also an indication of the similarity of two functions and is the frequency-domain analogy with correlation in the time domain.