What is a dendrogram in Hierarchical Clustering Algorithm?

A dendrogram is defined as a tree-like structure that is mainly used to store each step as a memory that the Hierarchical clustering algorithm performs. In the dendrogram plot, the Y-axis represents the Euclidean distances between the observations, and the X-axis represents all the observations present in the given dataset.

Image Source: Google Images

Please read the Wikipedia article for a better understanding of Dendrogram: