Any two points on a line may be used to denote it as a line.  Symbolically, this is expressed by an overbar with arrowheads at each end over two letters corresponding to points on the line.  Consequently, any of the following notations represent the line above:


The notations above are read as "Line AB," "Line BA," "Line AC," and so forth.


A ray is occasionally referred to as a half line.  Rays begin at one point and continue indefinitely in a single direction after passing through another point (reference illustration below):


Similar to the methodology described above, a single arrowhead overbar is used to denote a ray.  Accordingly, the ray above may be denoted as:


The notations above are read as "Ray DE" and "Ray DF" respectively.  The first letter represents the endpoint while the second letter represents another point on the ray.


A line segment is the portion of a line between two points (reference depiction below):


Line segments are represented by a single overbar with no arrowheads over the letters representing the two endpoints.  Consequently, the line segment above may be represented by either: