I’ve never heard of any other kind of floss besides dental floss. So either:
Not redundant.
Isn’t there a British term for cotton candy called Candy Floss?
I’ve heard the term “candy floss” (and think I may have even used it as a kid, despite being Canadian.)
There’s also thong bikinis – the proverbial “butt floss.” 
Crotalus beat me to it, but “embroidery floss” is a specific item in the needlework universe.
Don’t know about that, but there is an American term for candy floss called cotton candy. 
There’s also “The Mill on the Floss,” which has nothing to do with candy or oral hygiene.
Computer software is also not a redundant phrase. According to the Online Etymology Dictionary (which dates floss to 1759) software as a word has been around since:
We use the term **fairy floss ** here to refer to what is called cotton floss/cotton candy elsewhere.
If you have a hair in your mouth and you pull it out, but one of the hairs on your head disappears, then you’ve found mental floss.
FLOSS is also used as an acronym for “Free/Libre/Open-Source Software”; that is, software that is free in the liberty sense (as opposed to the no-cost sense) and is, therefore, released under a license that meets the OSI’s (Open Source Initiative) definition of open source.
This is something of a political compromise, a way to get the FSF (Free Software Foundation) folks and the OSI folks under the same tent so the nontechnical business and marketing types of the world aren’t terminally confused by two groups with two different agendas promoting what looks to them like the same thing. (It’s a matter of emphasis: The FSF folks want to emphasize freedom through access to source code, whereas the OSI folks want to emphasize technical advancement through widespread source review and contribution.) If you aren’t involved in developing or marketing FLOSS, it isn’t something you really need to worry about.
No, mental floss are ear swabs/ Q-Tips.
:wally
I’ve seen floss used as a term for a thong, but thats just me!
Floss can also be a verb in American urban slang (at least it was a few years back). To floss means to proudly show off the expensive stuff you own. For example in the song “My Love Don’t Cost a Thing” Jennifer Lopez sings:
You think you gotta keep me iced
You don’t
You think I’m gonna spend your cash
I won’t
Even if you were broke
My love don’t cost a thing
Think I wanna drive your Benz
I don’t
If I wanna floss I got my own
Even if you were broke
My love don’t cost a thing
What does ‘floss’ mean in the context of the title “The Mill on the Floss”?
The mill in question is situated on the river Floss (i.e. that’s the name of the river).
Oh. I suppose it would be pointless of me to ask why the river had that name.
(T.S. Eliot just liked it that way.)
Enola. Try not to use the putz smiley in General Questions. Thanks.
samclem GQ moderator
There was a dental dam on the river so they called it Floss.