This document provides an overview of Couchbase, a NoSQL database. It begins with defining what NoSQL is and how it differs from SQL databases in being non-relational, schema-less, and scaling horizontally. It then discusses Couchbase specifically, describing its architecture as a distributed key-value store that partitions data into buckets and virtual buckets. The document outlines how Couchbase provides high availability, easy scaling, and flexible data modeling. It also covers Couchbase SDKs, queries, and replication capabilities.