# Line (geometry)

## Straight figure with zero width and depth / From Wikipedia, the free encyclopedia

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In geometry, a **straight line**, usually abbreviated **line**, is an infinitely long object with no width, depth, or curvature, an idealization of such physical objects as a straightedge, a taut string, or a ray of light. Lines are spaces of dimension one, which may be embedded in spaces of dimension two, three, or higher. The word *line* may also refer, in everyday life, to a line segment, which is a part of a line delimited by two points (its *endpoints*).

Euclid's *Elements* defines a straight line as a "breadthless length" that "lies evenly with respect to the points on itself", and introduced several postulates as basic unprovable properties on which the rest of geometry was established. * Euclidean line* and

*Euclidean geometry*are terms introduced to avoid confusion with generalizations introduced since the end of the 19th century, such as non-Euclidean, projective, and affine geometry.