MySQL is an open-source relational database management system (RDBMS). It is widely used for managing and storing data. It is one of the most popular database systems in the world and is commonly used in web applications, especially those developed with the LAMP (Linux, Apache, MySQL, PHP) or LEMP (Linux, Nginx, MySQL, PHP) stack.

It provides a scalable and reliable platform for storing and retrieving data. It uses the Structured Query Language (SQL) for managing databases, which is a standard language for interacting with relational databases. SQL allows users to define the structure of the data, manipulate and retrieve the data, and perform various other operations such as creating, modifying, and deleting tables, as well as defining relationships between tables.

Some key features of MySQL include:

1. Relational Database Management: It follows the relational database model, allowing users to define relationships between different tables and perform complex queries to retrieve data.

2. Scalability: It can handle large amounts of data and supports various storage engines, which provide different features and optimizations for different use cases.

3. Performance: It is known for its high performance and efficiency. It has been optimized to handle concurrent operations and execute queries quickly.

4. Security: It provides various security features such as user authentication, access control, and encryption options to protect the data stored in the database.

5. Replication and High Availability: It supports replication, allowing you to create multiple copies of the database for redundancy and scalability. It also provides features for high availability, ensuring that the database remains accessible even in the event of failures.

MySQL is used in a wide range of applications, from small-scale websites to large enterprise systems. It is supported on various operating systems, including Windows, macOS, and Linux, and there are also numerous client libraries and tools available for interacting with MySQL databases.