In geometry, what is a vertex?

A vertex is defined as the point where two or more lines, edges, or rays meet. This concept is fundamental in geometry, applicable to both two-dimensional figures, such as triangles and polygons, and three-dimensional shapes, such as polyhedra. For instance, in a triangle, the corners where the sides intersect are each considered a vertex. This understanding is crucial as it forms the basis for many geometric properties and theorems. The other definitions provided do not accurately capture the meaning of a vertex, thus reinforcing why the first choice is the correct answer.