Php Notice: Undefined index: What does this mean?

[Findd Online]

Notice: Undefined index: points in C:\PHP Projects\Findd Online\quick_finish.php on line 43

Notice: Undefined index: product in C:\PHP Projects\Findd Online\quick_finish.php on line 44

My code....

<?php

//Variables
$Ad_Day = $_POST['points'];
$Product = $_POST['product'];

if(isset($Ad_Day))
{

}
else
{
die("You need to enter how long you will advertise!");
}

if(empty($Product))
{
die("What product to you want to advertise for?");
}

?>