PHP (Hypertext Preprocessor) is a widely-used, open-source scripting language primarily designed for web development. It is embedded within HTML, allowing developers to create dynamic, interactive web pages. PHP is server-side, meaning the code is executed on the server, and the result is sent to the browser as plain HTML. It supports various databases like MySQL and PostgreSQL, and is known for its simplicity, speed, and flexibility, making it ideal for developing websites, web applications, and APIs. Popular platforms like WordPress and Facebook have PHP at their core.