In
geometry,
parallel lines are
lines in a
plane which do not meet; that is, two lines in a plane that do not
intersect or
touch each other at any point are said to be parallel. By extension, a line and a plane, or two planes, in
three-dimensional Euclidean space that do not share a point are said to be parallel. However, two lines in three-dimensional space which do not meet must be in a common plane to be considered parallel; otherwise they are called
skew lines. Parallel planes are planes in the same three-dimensional space that never meet.