The crossword solution for the term 'song or 'SLUG' attachment' is FEST, a four-letter word. FEST is an acronym for File Exchange and Streaming Technology, which is a type of software used to attach audio files to websites. This technology allows users to easily upload and share music, podcasts, and other audio files with others. It is commonly used by musicians, podcasters, and other audio content creators to share their work with the world.