The lapping of one thing over another; as, an overlap of
six inches; an overlap of a slate on a roof.
When one is in a relationship that both people know is ending and one of the two people starts to look for another relationship. This could be described as [cheating] but is usually not recognized as such as both people know that the end of the current relationship is emminent.
When two people have hooked up with at least one person in common, usually used when the number is a lot more.
noun - the occurance of dating two people at one time, when one relationship is ending and anther is beginning.
verb - to have two dating relationships that are beginning and ending concurrently.
* These videos are coming directly from Youtube, they may or may not be most relevant to the word "Overlap"