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line

Basic element of Euclidean geometry. Euclid defined a line as an interval between two points and claimed it could be extended indefinitely in either direction. Such an extension in both directions is now thought of as a line, while Euclid's original definition is considered a line segment. A ray is part of a line extending indefinitely from a point on the line in only one direction. In a coordinate system on a plane, a line can be represented by the linear equation ax + by + c = 0. This is often written in the slope-intercept form as y = mx + b, in which m is the slope and b is the value where the line crosses the y-axis. Because geometrical objects whose edges are line segments are completely understood, mathematicians frequently try to reduce more complex structures into simpler ones made up of connected line segments.

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(1) A communications channel. See line card and port.

(2) In text-based systems, a row of characters.

(3) In graphics-based systems, a row of pixels.

The First Lines

This photo, taken at Broadway and Cortlandt Streets in New York in 1883, shows a nation exploding with its first communications. The very same thing is happening today with the Internet, only the infrastructure is not visible. (Image courtesy of AT&T.)

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line - 1. An electrical conductor. For distances larger than a breadbox, a single line may consist of two electrical conductors in twisted, parallel, or concentric arrangement used to transport one logical signal. By extension, a (usually physical) medium such as an optical fibre which carries a signal.