A Dendrogram is a variation of a Tree Diagram that illustrates the arrangement of clusters formed by hierarchical clustering. This is done to help visualise and classify the taxonomic relationships between entities related in a group.

Dendrograms are made up of branches, known as clades. These branches split into smaller branches, each ending in a point called a leaf. Each leaf represents an individual entity. Clades closer to the bottom of the diagram show individual entities, while higher clades represent groups of entities that have been clustered together. Clades that contain only a single leaf represent outliers, indicating entities that do not cluster closely with others.

The height of the branches represents the similarity or dissimilarity between entities or clusters. Two leaves or clades connected at a lower height are more similar to each other, whereas those connected at a higher height are more dissimilar. The greater the height difference between two clades, the more dissimilar they are.

Tools that can draw a Dendrogram:

Examples of a Dendrogram

Hierarchical clustering of cluster exemplars.
Affinity propagation clustering of Drosophila melanogaster neurons

Example 7, How to read a Dendrogram.
The Institute of Canine Biology

Fig 2, Dendrogram resulting from the hierarchical clustering analysis depicting five distinct assemblages with icons of dominant taxa using data analyzed from underwater videos. Taxa illustrations by Julia Mackin-McLaughlin.
A multi-scale feature selection approach for predicting benthic assemblages — ResearchGate