Undirected graph

An undirected graph consists of vertices joined by edges with no orientation, so each edge connects its endpoints symmetrically.

Graph theory: The mathematical study of graphs and their structural properties. Undirected graphs are one of graph theory’s two fundamental edge-orientation models.
Incidence matrix: A matrix recording which vertices are incident to which edges. It encodes undirected edge endpoints directly, including in multigraphs.
Path graph: A graph whose vertices form a single path, with consecutive vertices joined by edges. It is the simplest connected undirected graph with more than one vertex.
Social network: A network of people or groups connected by social relationships. Friendship and collaboration are often modeled as undirected links.
Directed graph: A graph whose edges have orientations from one endpoint to another. Unlike undirected edges, its connections distinguish source from destination.
Vertex (graph theory): An entity represented as a point in a graph. Vertices are the endpoints that undirected edges connect.
Adjacency list: A graph representation listing the neighbors of each vertex. Each vertex’s list records the other endpoint of every incident edge.
Cycle graph: A graph whose vertices form one closed cycle of edges. It adds a closing edge to a path, creating a simple loop.
Molecular graph: A graph representing atoms as vertices and chemical bonds as edges. Bond connectivity is commonly represented without orienting the bond edges.
Mixed graph: A graph containing both directed and undirected edges. It combines the two edge conventions separated by this graph type.

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