The condition of occupying the same place in space; as, the coincidence of circles, surfaces, etc.
the quality of occupying the same position or area in space; "he waited for the coincidence of the target and the cross hairs"
When two identical signals occupy the same point in space and time. They will sum to +6 dB if they have the same polarity. If one has an inverted polarity, they will cancel each other. Two signals which are not coincident will usually sum to +3 dB.