In geometry, two or more lines are said to be coincident when they occupy the same space without intersecting. That is to say, they are contained within the same plane and run parallel to one another. Coincident lines can also refer to two or more curves that intersect each other at multiple points throughout their length.

Any geometrical object for example two lines that are said to be exactly overlapping or an exact overlap of each other is known as coincident. There is no parallelism or perpendicularity between them, but their characteristics are perfectly similar.

Two lines or plane congruent geometric figures which lie on top of each other are said to be coincident.

Coincident lines are the lines that are on top of each other. They are neither parallel lines nor perpendicular lines but are completely similar. In other words, these are the lines in which one line completely covers the other line in such a way that we can't identify that there are two lines. Both lines appear to be a single line.

In Euclidean geometry, there are two types of coincident lines: parallel and concurrent. Parallel lines share the same orientation but never intersect each other; concurrent lines intersect at one point but otherwise have different orientations. In both cases, they are considered to be coincident because they pass through the same points in space.