Same Side Interior Angles

What are same-side interior angles? Interior angles are formed when a line, called transversal, cuts or intersects two or more lines.

In the figure below, line s is the transversal or the line that cuts or intersects two lines (line x and line y).

Same-side interior angles are located not only on the inside of the lines the transversal cuts, but also of course on the same side of the transversal or red line. 

Angle a and angle b are located on the same side of the transversal or line s and they are also located inside line x and line y. Therefore, angle a and b are called same-side interior angles.