PHP Filters are used to sanitize data coming from outside world inside your application.
PHP Filters
Why filters are used in PHP? - Computational complexity
RIPS Technologies on Twitter: "Be careful when using filter_var() for validating user input. Can you spot the vulnerability? #PHP #coding #codechallenge https://t.co/NM8r7DLl0k" / Twitter
How to validate and sanitize user input with PHP? - GeeksforGeeks