Coincidence

Coincidence literally describes two or more events or entities occupying the same point in space or time, but colloquially means two or more events or entities possessing unexpected parallels, when it is clear that there is no ordinary causal connection. The index of coincidence can be used to analyze whether two events are related. A coincidence does not prove a relationship, but related events may be expected to have a higher index of coincidence. From a statistical perspective, coincidences are inevitable and often less remarkable than they may appear intuitively. In optics, coincidence is also used to refer to two or more incident beams of light that strike the same point at the same time.