The overlap field of search results is only available when searching for a bounding box area of interest. When present, it contains details of the portion of the scene that is your area of interest. The Area field is the area of the scene that is part of your AOI (the overlap with your AOI)
Percent is a little different. Percent is the % of your total search AOI that this overlap satisfies (i.e. if you did a very large search and you may include most of the scene, but it may only be 25% of your search area).