Two or more lines are parallel when they lie in the same plane and never intersect. The symbol for parallel is <span>||</span>. To mark lines parallel, draw arrows <span>(>)</span> on each parallel line. If there are more than one pair of parallel lines, use two arrows <span>(<span>>></span>)</span> for the second pair. The two lines below would be labeled <span><span><span>AB</span><span>←→</span></span> || <span><span>MN</span><span>←→−</span></span></span> or <span>l || m</span>.
For a line and a point not on the line, there is exactly one line parallel to this line through the point. There are infinitely many lines that pass through A, but only one is parallel to l.
In three-dimensional geometry, skew lines are non-coplanar lines that do not intersect. For example, take a look at the first image I provided. Lines M and N do not lie on the same plane and they do not intersect with each other. That means that we can say line M is skew to line N.
In geometry, parallel lines are coplanar lines that do not intersect. For example, take a look at the second image I provided. Lines J and K lie on the same plane and they do not intersect with each other. This means that line J is parallel to line K.
