In the framework of Big Data Analytics, this lecture offers a thorough introduction to NoSQL databases. It discusses the definition and main distinctions between NoSQL and SQL, looks at situations in which NoSQL is useful, and lists several NoSQL database types, including MongoDB, Cassandra, Redis, HBase, and Neo4j. To emphasize NoSQL's place in contemporary, scalable, and high-performance data systems, the CAP Theorem, benefits, drawbacks, and practical applications—such as real-time analytics, the Internet of Things, and e-commerce—are also covered.