Distributed Computing Seminar Lecture 4 provided an overview of clustering algorithms and techniques. It discussed how clustering is used to group related data in applications like Google News and Amazon. It described hierarchical and partitional clustering algorithms and the k-means clustering algorithm. The lecture also introduced canopy clustering as a preliminary step that can help parallelize computation for clustering large datasets using MapReduce. It provided an example of how to efficiently partition a large movie ratings dataset into clusters using canopy clustering, k-means clustering, and MapReduce.