MySQL is a relational database management system (RDBMS) that uses SQL (Structured Query Language) as the language for managing and manipulating data in a database. It is an open-source software and is widely used as a database server for various web-based applications, especially those using PHP.
MySQL was originally created by MySQL AB, a Swedish company, and later acquired by Oracle Corporation. It is a popular choice for many web applications due to its speed, scalability, and ease of use. MySQL supports a wide range of platforms and operating systems, including Linux, Windows, and macOS, and it is available in both a community edition and an enterprise edition.
MySQL offers a variety of features, including support for ACID-compliant transactions, replication, triggers, stored procedures, views, and a variety of storage engines. It is also highly customizable, with the ability to create custom functions and plugins.
MySQL is widely used in web applications, content management systems, and e-commerce platforms, among other applications. It is also used by many popular websites, including Facebook, Twitter, and YouTube.

The choice between MySQL and PostgreSQL often depends on the specific needs of the project or application. Both MySQL and PostgreSQL are popular open-source relational database management systems, but they have different strengths and weaknesses.
MySQL is generally known for its speed and ease of use, particularly when it comes to read-heavy workloads. It has a wide range of features, including a variety of storage engines, replication, and support for triggers, stored procedures, and views. MySQL is particularly well-suited for web-based applications that require high performance and scalability.
PostgreSQL, on the other hand, is known for its robustness, reliability, and support for advanced features such as transactions and concurrency control. It is considered more suitable for complex applications with high-volume writes, and is particularly popular in scientific, financial, and government applications.
Both MySQL and PostgreSQL have large and active communities of developers and users, so there is a lot of documentation and support available for both databases. Ultimately, the choice between MySQL and PostgreSQL will depend on the specific needs of the project, as well as the skillset and preferences of the development team.