Vertex
There are multiple uses of the word vertex in mathematics, including uses in graph theory and multiple uses in geometry.
Vertex of a parabola
The vertex of a parabola is the point which, if a vertical line is placed over it, divides the parabola into two equal mirror images. The vertex occurs at either the maximum value or the minimum value of the graph, depending on the coefficient of 
. If it is positive, then the vertex lies at the minimum of the graph. If it is negative, then the vertex lies at the maximum of the graph.
Vertex of an angle
See angle.
Vertex of a polygon or polyhedron
See polygon.
Note that the plural form of the word "vertex" is the word "vertices;" the singular of "vertices" is "vertex," not "vertice."
