Summary

NoSQL databases store data without fixed tables. They are schema-less and optimized for horizontal scaling. Common types include key-value, document, column-family, and graph. Typical use cases: large-scale web apps, real-time analytics, and content storage. Many systems favor eventual consistency over strict ACID transactions. sharding and replication are core patterns. Remember the CAP theorem: you can choose any two of Consistency, Availability, and Partition tolerance in a distributed system.