What is PHP?
PHP stands for 'Hypertext Preprocessor' which is actually a recursive acronym. It is an open source programming language for the web. In other words, PHP is a server side scripting language that can be embedded into HTML code, then parsed and processed when the page is requested by a client.
Don't get confused when we use the term 'scripting language' instead of calling PHP a programming language. It means the same.
Why is PHP so popular?
Because of it being an open source programming language and its ease of use. Practically, PHP is much easier to learn and code when compared to other programming languages. It is fast and flexible. Like every other language, there is a certain degree of learning curve associated with PHP. Refer to features of PHP.
Where to get started with PHP?
Before you start with basics of PHP programming, it is important that you understand the purpose and usability of programming in PHP. You should know what you can achieve with PHP and what it is not meant for.