Which geometric concept involves dividing an angle into two equal parts?

The concept of dividing an angle into two equal parts is specifically described by the term "angle bisector." An angle bisector is a ray that starts at the vertex of the angle and extends outward, effectively splitting the angle into two angles that are congruent, meaning they have the same measure. This is crucial in geometry, as it helps with various constructions and proofs where equal angles are necessary.

The other terms do not describe this action. A transversal is a line that intersects two or more lines at different points, often used in the context of parallel lines to create angles, but it does not involve dividing an angle. A congruent angle refers to angles that have the same measure, but this term does not imply any specific action of dividing. A vertex is simply the point where two sides of an angle meet, again not related to the concept of dividing an angle. Understanding the role and definition of the angle bisector is fundamental in geometry, especially in angle relationships and triangle constructions.