A story based on the lyrics of a song, with the lyrics inserted into the fic. This is not to say that every story that has lyrics in it is a songfic. Songfics are those stories which depend so heavily on the lyrics that the story could not possibly make sense without the lyrics as reference. Songfics tend to be horrible and pointless, and some archives and mailing lists ban them.
Using a song's lyrics as a background
a fic set around or themed against a songg. Songfics are almost always titled after the song in question and include the actual lyrics interspersed throughout the story.
A fic written around lyrics, usually to a romantic song that mirrors the feelings or emotions of a character. (See also "lyric fic.")
fic based on/incorporating the lyrics to a song. generally very very bad. problems start with the almost-certainty that the reader either won't know the song or won't have the same emotional response. for instance, how many of you have heard the song 'nostalgia'? exactly. songfics are often written to sappy lovesongs. i've never seen a songfic i've liked. the absolute most i've seen work is a couple of lyrics thrown in as dialogue/narrative or as the title of the fic.
a fanfic that has song lyrics added in to enhance it
Fanfiction inspired by/heavily laden with song lyrics. Ms. Nitpicker strongly recommends against this practice, outside of music wheel circles, since she is unfamiliar with 90% of the songs involved and therefore the intended impact of the piece is totally lost. Unless the actual music is unimportant and you only intend for us to be moved by the great lyrics, songfic is difficult to successfully churn out. However, this is a popular genre of fanfic.
A story with song lyrics woven into a story, can also include stories inspired by a particular song. The basic thing to remember when writing songfic is that if your story can not stand without the song lyrics it will most likely not be better with them. Always take a good look at the piece without the lyrics to make sure you have written a cohesive story that can be enjoyed even if the reader has never heard the song you have in mind.
A songfic is a work of fiction set to the lyrics of a particular song. The term is derived from "song" and "fiction"; as such, one might also see the genre referred to as "songfiction". Songfics are a genre of artwork related to fanfiction in that both involve the poaching of text.