Definition
Parallel lines
Parallel lines are coplanar lines that stay the same distance apart and never meet.
Continue from this idea into connected AXIO math.
What it means
Imagine two perfectly straight rails viewed from directly above. They keep the same gap everywhere. Even if you extend them forever in both directions, they never cross.
Remember it
Straight rails from above: one steady gap, no meeting point.
Example
On squared paper, draw one horizontal line along a row and another three rows above it. The lines remain three squares apart, so they are parallel.
Watch for
Lines that would meet when extended are not parallel, even when the visible pieces do not touch.
Common mix-up
Lines can point in the same general direction yet still move closer together; only a constant gap makes them parallel.
Exact meaning
In Euclidean geometry, two distinct coplanar lines are parallel when they do not intersect; equivalently, their perpendicular separation remains constant.