What defines vertical angles?

Vertical angles are formed when two straight lines intersect, creating pairs of angles that are opposite each other. This characteristic means that for every intersection of two lines, there are two pairs of vertical angles. They share a vertex and are formed in such a way that each angle of one pair is opposite the angle of the other pair. One key property of vertical angles is that they are always equal in measure; if one angle is 50 degrees, the angle directly across from it (its vertical angle) will also be 50 degrees. This distinctive feature of vertical angles is fundamental in various geometric proofs and problems, making this answer the correct one.