The state of things overlapping or piling on top of each other; can also refer to overlaps in time or scope.
書類の重なりで重要なページを見落とした。
I missed an important page because the documents were overlapping.
二つの会議の時間が重なり、どちらに出席するか迷っている。
The two meetings overlap in time, and I'm unsure which to attend.
色の重なりがこの絵の魅力を生んでいる。
The overlapping of colors creates the appeal of this painting.