Bindings is a TIdSocketHandles property and a collection of TIdSocketHandle instances. For TIdUDPServer, Bindings will contain TIdSocketHandles instances with an allocated socket type of ID_SOCK_DGRAM. 

Bindings provides the DefaultPort number for the TIdUDPServer and is used by the TIdUDPListenerThread to gain access to the socket handle and low-level access methods provided by the protocol stack. 

Use Bindings to create socket bindings for servers with multiple network adapters (Host addresses), or which listen on multiple Port numbers.

DefaultPort 

TIdSocketHandles 

TIdSocketHandle 

TIdUDPListenerThread