Angles located inside the two lines intersected by a transversal.
Examples
In the case of intersecting lines :
In the case of parallel lines cut by a transversal :
In the figures above, angles 3, 4, 5 and 6 are interior angles.
In the case of intersecting lines :
In the case of parallel lines cut by a transversal :
In the figures above, angles 3, 4, 5 and 6 are interior angles.