SWD file is a Shockwave Flash Debug File. SWD files are similar to SWF files, except that they contain debugging-specific information that the debugger and Flash Debug Player watch for.

Common .swd file type descriptions:

Flash Debug File
Flash-Debugging-Datei
File di debug di Flash
Файл отладки Flash
Arquivo de depuração Flash

Applications, associated with .swd files

Adobe Flash by Adobe Systems®, Incorporated

.swc

.swf