PHP is a commonly used open-source, server-side scripting language that was specifically designed for web development and can be used within HTML directly. What differentiates PHP from a client-side language such as JavaScript, is that the code is carried out on the server, after which HTML code is generated that is then sent to the client. The client receives the results from the script, but doesn’t know what the underlying code was. This makes it easy for the code that is carried out to stay hidden to users.