They are lines that run alongside each other that never intersect.
When transversal line t intersects parallel lines a and b, it makes the same-side interior angles 3 and 6 supplementary. Same-side interior angles 4 and 5 are also supplementary. Supplementary angles are angles that add up to 180 degrees.
The same-side interior angle theorem states that when two lines that are parallel are intersected by a transversal line, the same-side interior angles that are formed are supplementary, or add up to 180 degrees.
