A dendrogram (from Greek dendron "tree", -gramma "drawing") is a tree diagram frequently used to illustrate the arrangement of the clusters produced by hierarchical clustering. Dendrograms are often used in computational biology to illustrate the clustering of genes.

For a clustering example, suppose this data is to be clustered using Euclidean distance as the distance metric.

The hierarchical clustering dendrogram would be as such:

Here the top row of nodes represent data, and the remaining nodes represent the clusters to which the data belong, and the arrows represent the distance.