Graph clustering is a technique used to group nodes in a graph into clusters or communities based on their connections. Each cluster contains nodes that are more closely related to each other than to those in other clusters. This helps in identifying patterns and structures within the data represented by the graph. The process of graph clustering can be applied in various fields, such as social network analysis, where it helps to find groups of friends or communities. It is also useful in machine learning and data mining for simplifying complex data sets and improving the efficiency of algorithms.