A vertex is a point where two or more lines, edges, or rays meet. In geometry, it is commonly used to describe the corners of shapes, such as triangles and polygons. For example, a triangle has three vertices, while a square has four. Each vertex is a crucial part of the shape's structure. In graph theory, a vertex represents a fundamental unit in a graph, which can be connected to other vertices by edges. This concept is essential for understanding networks, such as social networks or computer networks, where vertices can represent individuals or devices, respectively.