CODE EXAMPLE FOR PHP

what does ? mean in PHP

/* 
in php, ? is the 'Ternary Operator'.

The expression (expr1) ? (expr2) : (expr3) evaluates 
to expr2 if expr1 evaluates to true, and expr3 if 
expr1 evaluates to false.

It is possible to leave out the middle part of the 
ternary operator. Expression expr1 ?: expr3 evaluates 
to the result of expr1 if expr1 evaluates to true, 
and expr3 otherwise. expr1 is only evaluated once in 
this case.
*/

<?php
// Example usage for: Ternary Operator
$action = (empty($_POST['action'])) ? 'default' : $_POST['action'];

// The above is identical to this if/else statement
if (empty($_POST['action'])) {
    $action = 'default';
} else {
    $action = $_POST['action'];
}
?>