A PHP and MySQL application is a software system developed using two key technologies: PHP (Hypertext Preprocessor) and MySQL (Structured Query Language).

PHP is a popular server-side scripting language used for creating dynamic web pages and web applications. It enables developers to embed PHP code directly within HTML, allowing for the generation of dynamic content, data processing, and interaction with databases.

MySQL, on the other hand, is an open-source relational database management system. It provides a platform for storing and retrieving structured data efficiently. MySQL uses the SQL language to manage databases, enabling developers to create, modify, and query data stored in tables.

In a PHP and MySQL application, PHP scripts handle user requests on the server-side. These scripts can dynamically generate HTML content, process user input, and interact with the MySQL database to store, retrieve, update, or delete data. This combination of technologies is widely used for building a variety of web applications, ranging from simple content management systems and e-commerce platforms to complex social networks and data-driven web applications.