The difference between empty and isset in php

/**
* isset — Check whether a variable is set
* Return true if the variable exists, false otherwise
*
* empty — Check whether a variable is empty
* If the variable is a non-empty or non-zero value, empty() returns false
**/
$is_var = '';
if (isset($is_var)) {
 echo "The variable exists!";
} else {
 echo "The variable does not exist!";
}
< ;p>if(empty($is_var)) {
 echo "The variable is empty!";
} else {
 echo "The variable is not empty!";
}
 ?>

Output results: The variable exists! The variable is empty!