An undirected graph is a collection of points, called vertices, connected by lines, known as edges. In this type of graph, the edges do not have a direction, meaning that the connection between any two vertices is bidirectional. For example, if vertex A is connected to vertex B, you can travel from A to B and from B to A without any restrictions. Undirected graphs are commonly used in various fields, including computer science and social network analysis. They can represent relationships where direction is not important, such as friendships in a social network or connections in a transportation system.