Parallel lines never meet. No matter how far you extend them, they stay the same distance apart — like train tracks running off into the horizon.
Perpendicular lines meet at exactly 90°. The crossing point always forms four right angles.
When a third line crosses two parallel lines, it creates pairs of equal angles. Corresponding angles (in matching positions at each crossing) are always equal. Alternate interior angles (on opposite sides, between the parallel lines) are always equal too.
Remember
Parallel = never meet. Perpendicular = meet at 90°. These are two very different relationships.
Real World
The lines on lined notebook paper are parallel. The margin line crossing them is perpendicular — forming right angles where they meet.
Feeling ready?
Put this concept to work with a practice workout.