A dendrogram is a tree-like diagram that visually represents the arrangement of clusters or groups in data analysis. It is commonly used in fields like biology for displaying the evolutionary relationships between species, as well as in statistics for hierarchical clustering, which organizes data points based on their similarities. In a dendrogram, each branch represents a cluster, and the length of the branches indicates the distance or dissimilarity between the groups. The diagram helps researchers and analysts easily interpret complex data structures, making it a valuable tool for understanding relationships in various datasets, including genetic data and social networks.