The vertex is otherwise known as?

The vertex is defined as the point of intersection of two lines. In geometry, the term "vertex" commonly refers to the point where two edges or lines meet, such as the corners of a polygon or the angles formed between two intersecting lines. This is a fundamental concept in both geometry and trigonometry, where understanding the properties and relationships involving lines and angles is crucial.

The other options reference different concepts that do not accurately describe the vertex. A 30, 60-degree triangle does not relate to the concept of a vertex specifically; instead, it refers to a specific type of triangle with set angle measurements. An angle formed by two lines describes an angle but does not point to the specific intersection as the vertex does. Finally, a starting point of an ellipse refers to different geometric construction, typically associated with ellipses and their foci, which is unrelated to the straightforward definition of a vertex.