Definition: In English, "modify" means to make or change something; "replace" means to substitute another thing for one that exists already; "php" stands for "PHP (Python Hypertext Preprocessor)", a language that's used on web sites. So, 'modifier.replace.php' is a phrase or command that modifies or replaces an existing piece of PHP code with another. It usually involves syntax and/or logic manipulation to make the modified code more readable and usable by users who might be unfamiliar with PHP (or any other programming language).