This document provides an introduction to unsupervised learning, including defining unsupervised learning and how it differs from supervised learning. It discusses common unsupervised learning techniques like clustering, dimensionality reduction, K-means clustering, hierarchical clustering, principal component analysis (PCA), and t-distributed stochastic neighbor embedding (t-SNE). The document explores applications of unsupervised learning and its importance in extracting patterns from unlabeled data to gain hidden insights.