What is the “item_description=” for ?

Hi,
If I add the “item_description=” tag, I do not see it used anywhere. What is it for ?

The whole idea of showing the customer what she is going to pay for is quite nice, I’d be glad to see how to implement this ?
I tried both Credit Card and Paypal account payments, nothing seems to show this value. Even the order recorded in the “Orders” page does not show it.

Thanks for your assistance & regards
Thierry