Warning

A warning is a non-fatal runtime error that alerts developers about a problem in the code, but doesn’t stop script execution at that point.

Warnings are one of the error reporting levels, between error and notice.

<?php

include 'unknown-file.php'; // Warning, failed to open stream unknown-file.php

?>

Documentation

See also Dealing with Warnings in PHP, the Right Way.

Related : Error, Notice, Error Reporting, Fatal Error