No, same side interior angles are not necessarily congruent. Same side interior angles are formed when two parallel lines are intersected by a transversal. These angles are located on the same side of the transversal and inside the parallel lines.
However, same side interior angles are supplementary, meaning they add up to 180 degrees. This is a key property of same side interior angles when dealing with parallel lines and a transversal.
For example, if one same side interior angle measures 110 degrees, the other same side interior angle will measure 70 degrees, making the total 180 degrees. This supplementary relationship is what defines same side interior angles, not congruence.