Vertical angles, vertically opposite angles

Vertical angles,

vertically opposite angles

Vertical angles are the angles that lie opposite to each other when two lines intersect.

Two vertical angles always share a common vertex. However, they never share a common side (arm).

«Vertical» in this case means they share the same Vertex (corner point), not the usual meaning of up-down.

Example: 
∠AOD and ∠BOC are vertical angles. ∠AOC and ∠BOD are vertical angles.
 
Vertical angles are congruent (the same number of degrees)