what is php

echo "Hello World";

PHP is a server side scripting language. It is open source. It is embedded language. 

PHP is a general-purpose scripting language especially suited to web development. It was originally created by Danish-Canadian programmer Rasmus Lerdorf in 1994; the PHP reference implementation is now produced by The PHP Group
Implementation language: C (primarily; some components C++)
Stable release: 7.4.11 / October 1, 2020; 5 days ago
Preview release: 8.0.0 Release Candidate 1 / October 1, 2020; 5 days ago
Typing discipline: Dynamic, weak since version 7.0: Gradual
Designed by: Rasmus Lerdorf
Developer: The PHP Development Team, Zend Technologies 

PHP is an acronym for "PHP: Hypertext Preprocessor" PHP is a widely-used, open source scripting language. PHP scripts are executed on the server.

PHP is a scripting language normally used by web developers to build websites.
It supports object oriented programming.
It even has support for building windows desktop applications with PHP Desktop

PHP stood for Personal Home Page now it stands for Hypertext Pre-processor.
PHP is an open-source, interpreted, and object-oriented scripting language that can be executed at the server-side. 
PHP is well suited for web development. Therefore, it is used to develop web applications (an application that executes on the server and generates the dynamic page).
PHP was created by Rasmus Lerdorf in 1994 but appeared in the market in 1995.Most of PHP syntax is based on C. It is used to manage dynamic content, databases, session tracking, even build entire e-commerce sites.
PHP is powerful enough to be at the core of the biggest blogging system on the web (WordPress)!
PHP is deep enough to run the largest social network (Facebook)!
PHP is also easy enough to be a beginner's first server side language!

PHP is a server side scripting language. that is used to develop Static websites or Dynamic websites or Web applications. PHP stands for Hypertext Pre-processor, that earlier stood for Personal Home Pages. PHP scripts can only be interpreted on a server that has PHP installed.