Each address associated with a customer (including the Contact Address) may have a short (25 character maximum) descriptive Address Label. Examples of Address Labels are "Home", "Work", "Mom", "Aunt Beth", etc.
If the Multiple Ship To option (Settings/Boolean Options) is on, customers who have logged in, as well as customers who are not logged in but are recognized by a cookie upon entry to your Online Store, see their "Ship To" select boxes on Product List and Detail screens pre-populated with all available Address Labels, including the label of the Contact Address, if applicable.
If any of those pre-populated addresses is used, the full address is also pre-populated on the Ship To/Bill To screen; if all addresses in use match, then recognized labels and/or appropriate default addresses can be used, and the customer may bypass the Ship To/Bill To screen altogether.
Address Labels are also displayed when a customer accesses his/her address book from the Ship To/Bill To screen.