What is a recursive acronym?

The answer

A recursive acronym is an abbreviation in which one of the letters stands for the abbreviation itself. PHP is a well-known example, because the first P in PHP: Hypertext Preprocessor expands to PHP again, so the expansion could be repeated endlessly. The PHP manual describes the name in this way. It is a small joke, but it also makes the name easy to remember, and it is a common viva and interview question for beginners.