What Are the Terminologies of Graph in Data Structure?


Larry Thompson

Graphs are an essential data structure used in computer science and mathematics to represent relationships between objects. Understanding the terminologies associated with graphs is crucial for effectively working with them. In this article, we will explore some of the key terminologies of graphs and their significance.


A vertice, also known as a node, is a fundamental building block of a graph. It represents an object or an entity. Each vertice in a graph can be connected to one or more other vertices through edges.


An edge is a connection between two vertices in a graph. It represents the relationship or link between the connected vertices. Edges can be directed, meaning they have a specific direction, or undirected, where they do not have any direction.


In some graphs, edges can have weights associated with them. The weight represents the cost or distance between the connected vertices. Weighted graphs are commonly used in applications such as network routing and optimization problems.

Directed Graph

A directed graph, also known as a digraph, is a type of graph where each edge has a specific direction. The direction indicates the flow or relationship between the connected vertices. In a directed graph, it is possible to have one-way connections between vertices.

Undirected Graph

In contrast to directed graphs, undirected graphs do not have any specific direction associated with their edges. The relationship represented by an edge is bidirectional, meaning it can be traversed in both directions.


A cycle in a graph refers to a path that starts and ends at the same vertex without passing through any other vertex more than once. Cycles are important because they provide insights into connectivity and allow for the detection of loops or repetitive patterns in a graph.

Connected Graph

A connected graph is one where there is at least one path between any pair of vertices. In other words, we can reach any vertex from any other vertex in the graph by following a series of edges. Connected graphs are essential for ensuring that all vertices are reachable and interconnected.

Disconnected Graph

In contrast to connected graphs, disconnected graphs have one or more isolated components. These components are sets of vertices that are not connected to the rest of the graph. Disconnected graphs can be useful in situations where we want to represent independent entities or separate systems.


A subgraph is a subset of vertices and edges that is derived from an existing graph. It contains only a portion of the original graph’s vertices and edges but maintains their relationships and connectivity. Subgraphs are useful for isolating specific portions of a larger graph for analysis or manipulation.

Adjacency Matrix

An adjacency matrix is a square matrix used to represent the connections between vertices in a graph. Each cell in the matrix represents an edge, and its value indicates whether an edge exists between two vertices or not. Adjacency matrices provide a convenient way to visualize and analyze the relationships in a graph.

Adjacency List

An adjacency list is another common representation of graphs. It uses an array or dictionary-like structure to store each vertice’s connections as a list or linked list. Adjacency lists are more memory-efficient than adjacency matrices for sparse graphs, where only a few edges exist.

In Conclusion

These are some of the key terminologies associated with graphs in data structure. Understanding these terms will help you navigate through various algorithms and operations performed on graphs efficiently.

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