  The interference observed for a quanton, traversing more than one path, is
believed to characterize its wave nature. Conventionally, the sharpness of
interference has been quantified by its visibility or contrast, as defined in
optics. Based on this visibility, wave-particle duality relations have been
formulated for two-path interference. However, as one generalizes the situation
to multi-path interference, it is found that conventional interference
visibility is not a good quantifier. A recently introduced measure of quantum
coherence has been shown to be a good quantifier of the wave nature. The
subject of quantum coherence, in relation to the wave nature of quantons and to
interference visibility, is reviewed here. It is argued that coherence can be
construed as a more general form of interference visibility, if the visibility
is measured in a different manner, and not as contrast.
