Lines that meet at a point are called intersecting lines.
Lines that always remain the same distance apart and never meet are called parallel lines.
A line that intersects two or more lines at distinct points is called a transversal.
When two lines are intersected by a transversal, pairs of corresponding angles, alternate angles and interior angles are formed.
Angles formed on the same side of a transversal, on the same side of the two lines and at corresponding vertices are called corresponding angles.
Angles formed on the opposite sides of the transversal at the two distinct points of intersection and between the two lines are called alternate interior angles.
Angles formed on the opposite sides of the transversal at the two distinct points of intersection but outside the two lines are called alternate exterior angles.
Angles that have different vertices, lie on the same side of the transversal and are interior angles are called consecutive interior angles or allied or co-interior angles.
Each pair of interior angles on the same side of the transversal are supplementary, each pair of corresponding angles are equal and each pair of alternate interior angles are equal. If a transversal cuts two lines such that the pairs of corresponding angles are equal, then the lines are parallel.