Lines
This is the number of pairs of parallel sides a regular octagon has.
What is 4?
This is the angle that is on the opposite side of an acute or obtuse angle.
What is a reflex angle?
In this quadrilateral you can find 4 pairs of perpendicular sides, 2 pairs of sides that will never cross, and 2 pairs of equal sides.
What is a rectangle? (4 right angles, 2 pairs of parallel sides)