If you have two pieces of something, and one is covering a part of another, then they're overlapping.
Remember learning about Venn Diagrams in math class? You know, the two circles drawn overlapping each other, so that there's a space in the middle that they share. No? Well for you non-mathletes, overlapping can be just as simple. Two cookies stacked partially on top of each other are overlapping. And two lives that intersect at a certain point in time? They're overlapping, too.
