Found in the following dictionaries
OTCWL2014 (NASPA Word List 2014)
TWL06 (NASPA List 2006)
TWL06 (NASPA List 2006)
"Filk" Definition
noun
Filk music.
Source: Wiktionary
Filk song.
Source: Wiktionary
adjective
About or inspired by science fiction, fantasy, horror, science, and/or subjects of interest to fans of speculative fiction; frequently, being a song whose lyrics have been altered to refer to science fiction; parodying. (However, much filk music is original rather than parodic.).
Source: Wiktionary
verb
To participate in a filk circle, including singing along.
Source: Wiktionary
To perform filk music.
Source: Wiktionary
To write a parody of (a song). Compare noun in construction "filk of...".
Source: Wiktionary