Ray (geometry)

A ray is part of a line that begins at one endpoint and extends infinitely in one direction. It is named by its endpoint and another point on it.

Point (geometry): An exact location in space with no dimensions. A ray begins at a single point that serves as its endpoint.
Directed line: A line equipped with a chosen direction of travel. A ray can be viewed as the forward half of a directed line starting at its endpoint.
Euclidean geometry: The study of geometry based on Euclid’s postulates, including ordinary lines, points, and angles. Rays are standard objects in Euclidean constructions and proofs.
Ray (optics): An idealized path along which light energy propagates in geometrical optics. The optical term models light direction, while the geometric ray is a set of points.
Line (geometry): A straight path extending infinitely in both directions. A ray shares a line’s straightness but extends in only one direction.
Cartesian coordinate system: A system that locates points using signed distances along perpendicular axes. Coordinates describe a ray by its endpoint and the direction in which it extends.
Compass-and-straightedge construction: A geometric construction using only a compass and an unmarked straightedge. Constructed angles and figures are defined using rays and their intersections.
Segment (mathematics): A portion of a mathematical object bounded by two points. A segment is finite and bounded at both ends, unlike a geometric ray.
Line segment: A part of a line bounded by two endpoints. Unlike a segment, a ray has only one endpoint and no finite end.
Vector (geometry): A quantity represented geometrically by magnitude and direction. A direction vector can specify every point reached from a ray’s endpoint.

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