An overlap happens when two or more things share a part that belongs to each other. Imagine wearing two shirts and having them both cover your shoulders.
You see overlaps all around you, from everyday life to technical terms. When you're working on a project, an overlap might occur if the deadlines for finishing one task bleed into another. Your schedule can get messy when one meeting ends right as another starts, creating overlap in your time slots.
How common is "overlap"?
Word overlap is considered uncommon in modern English. It has a balanced usage among all categories: speech, fiction, newspapers and academic texts.
Definitions
verb
To extend over and partly cover something.
Example: The mouse-mat overlapped the edge of the desk.
To co-occur, to happen at the same time.
To have an area, range, character or function in common.
Example: The two maps overlapped at the east and west edges.
(mathematics) Of sets: to have some elements in common.
Example: The set (all men) overlaps the set (vegetarians).
(genetics) To have some similar nucleotide sequences.
(art) An illusion of depth is created when one object partially covers another.