NoSQL (Not Only SQL) refers to a broad category of database management systems that differ from traditional relational databases in their data storage models, querying methods, and scalability approaches. NoSQL databases are designed to handle diverse data types and large-scale distributed systems, providing solutions for scenarios where traditional relational databases may encounter limitations.

Key characteristics of NoSQL databases include:

Flexible Data Models: NoSQL databases accommodate various types of data structures, including key-value pairs, documents, graphs, and wide-column stores. They allow for schema-less or schema-flexible designs, providing agility in handling unstructured or semi-structured data.

Scalability: NoSQL databases are designed for horizontal scalability, allowing users to distribute data across multiple servers (cluster or nodes) to handle high volumes of data and concurrent user requests more efficiently.

High Performance: They often prioritize performance and can offer high throughput and low latency, making them suitable for real-time data processing and applications requiring fast data access.

No Complex Joins: Unlike relational databases that rely heavily on complex joins for data retrieval, NoSQL databases often denormalize data or use different mechanisms to achieve data retrieval without complex joins.

CAP Theorem Consideration: NoSQL databases often focus on either consistency, availability, or partition tolerance (according to the CAP theorem) to suit specific application requirements, allowing trade-offs between these characteristics.

Use Cases: NoSQL databases are commonly used in various scenarios such as content management systems, e-commerce, real-time analytics, IoT, gaming, social media, and applications dealing with large amounts of data or distributed environments.