In 3D computer graphics, a vertex is a point in 3D space with a particular location, usually given in terms of its x, y, and z coordinates. It is one of the fundamental structures in polygonal modelling: two vertices, taken together, can be used to define the endpoints of a line; three vertices can be used to define a planar triangle. Vertices are commonly confused with vectors because they can be described with the same properties. They are, however, two completely different things.
In Astrology, the Vertex is a point in 3D space, seen near the Eastern horizon and the Ascendant in the (two-dimensional) starchart. Planets close to it lend their personality to the event(s) the chart captures.