Vertex

   

Vertex [vur-teks]
Noun
Plural: vertices [vur-tuh-seez]

A vertex is a common endpoint of two or more rays/line segments. 

Usually a vertex is a point/location where 2 lines meet.They are extremely important, a necessity in geometry especially when talking about shapes and figures. They can be used in 2D (a square has four vertices) and even with solid geometry, where since it is in a 3D plane, vertices are the point where 3 or more edges meet. Also in solid geometry, a vertex can also be called a corner.