Question

A pair of non-adjacent angles formed by two intersecting lines are called angles.

Answer 1

$\underset{–}{\text{Vertical Angles:}}$
Vertical angles are the pairs of opposite angles made by intersecting lines.

In the above figure, the pairs of vertical angles are:
$\bullet$$\angle 1$ and $\angle 3$
$\bullet$$\angle 2$ and $\angle 4$

Clearly, they are not adjacent and their sides are formed by two intersecting lines $AC$ and $BD$.