Wiktionary
n. (context idiomatic English) A difference, albeit vague and difficult to discern.
Wikipedia
"Fine Line" is a song from Paul McCartney's 2005 album, Chaos and Creation in the Backyard. McCartney plays all the instruments on the song including drums, bass, and piano. It was released 29 August 2005 as the first single from the album in the UK (see 2005 in British music). It reached number 20 on the UK Singles Chart and number 31 on the US Adult Contemporary. It also reached number 1 in Japan.
A live version is also featured on The Space Within US concert DVD from 2006.
"Fine Line" is a 1984 single by Barry Gibb. The song was written by Gibb and keyboardist George Bitzer. It is the second and final single from his debut solo album Now Voyager. It was released on October 1984 in North America by MCA Records and in most countries by Polydor Records. The song was failed to chart in the United States, but it did manage to reach #50 on the Hot Dance Club Songs. The 12" version of this song was remixed by Larry Patterson. This single was less successful than his previous single, " Shine, Shine".
Usage examples of "fine line".
Admittedly, there' an awfy fine line between the two, but good guys gettin' shot in the shoulder is the right side of it.
In those sessions you were walking a fine line, you were in the depths of hell.
He is a fine line officer except for this one understandable obsession and I should hate to lose him ….
For his entire adult life he had walked a fine line between respectability and notoriety: an alchemist without Guild connections could hope for little else.
There is a fine line between faith and common sense in some of this.