How would you define clustering? Can you name a few clustering algorithms?

$2.$ What are some of the main applications of clustering algorithms?

$3.$ Describe two techniques to select the right number of clusters when using k$-$means.

$4.$ What is label propagation? Why would you implement it$,$ and how?

$5.$ Can you name two clustering algorithms that can scale to large datasets? And two that look for regions of high density?

$6.$ Can you think of a use case where active learning would be useful? How would you implement it$?$