A DDE advise loop describes a connection back to the application that is used to track changes to a DDE topic. It instructs the server to inform the client when data in the server's application changes. Advise loops are set up across a conversation, and closing the conversation closes the advise loop.
An advise loop is identified by an item and a key. The key is included to allow any number of uniquely identifiable advise loops to be set up on the same server/topic/item combination.
A successfully established advise loop is also known as a link. When a change occurs to item, the link informs the client by causing it to execute a function.
There are two types of link: the warm link which only informs the client that a change to item has occurred, and the hot link which also sends the new data across.
Note: a DDE advise loop is not a loop in the program source code. In particular it should not be confused with the "event loop" which is a loop in source code that processes low level events.
LispWorks User Guide and Reference Manual - 21 Dec 2011