PHP (Hypertext Preprocessor) is a widely-used, open-source server-side scripting language primarily designed for web development. It is embedded within HTML to create dynamic and interactive web pages. PHP is known for its simplicity, flexibility, and ability to interact with databases like MySQL, making it a popular choice for building web applications and content management systems (e.g., WordPress). It supports features like session management, file manipulation, and data handling, and can be run on various platforms, including Windows, Linux, and macOS.