TIdDiscardUDPServer = class(TIdUDPServer);

TIdDiscardUDPServer is a TIdUDPServer descendant that implements a UDP-based server for the Discard Protocol, as described in the Internet Standards document: 

RFC 863 - Discard Protocol  

TIdDiscardUDPServer is a useful debugging and measurement protocol where the data sent to the server is simply discarded. TIdDISCARDServer provides a default implementation that accepts threaded client connections, reads the connection for the TIdPeerThread to determine it's InputBuffer contents, and discards the values. The threaded client connection automatically terminates after reading the InputBuffer.