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Definition of parallel for Students. 1  1 : a line or surface that lies at or moves in the same direction as another but is always the same distance from it. 2  2 : one of the imaginary circles on the earth's surface running in the same direction as the equator and marking latitude.
More Geometry Lessons. Parallel and Skew Lines. Parallel lines are two lines in the same plane that never intersect. In a coordinate plane, parallel lines can be identified as having equivalent slopes. Parallel lines are traditionally marked in diagrams using a corresponding number of chevrons (or arrows).