Voronoi Diagrams split an area up with polygons that each have a generating point. Each subsequent point in the polygon is closer to the generating point than any other.

Voronoi diagrams and Delaunay triangulations are related to each other, but aren't the same as shown by these comparison images:

This is an example of a Voronoi diagram, source

This is an example of a Delaunay triangulation, source.

As you can see, both of the previous images are from the same original image, but each are unique due to the choice of using Vonoroi diagrams vs Delaunay triangulations.