@dallin

From @danielst 's gnu.org link on the usage of 'FOSS':

'If neutrality is your goal, “FLOSS” is better. But if you want to show you stand for freedom, don't use a neutral term.'

If I was writing it out in full I would tend to write 'Free/Libre and Open Source Software' so I have a preference for 'FLOSS' but didn't realise that the GNU Project preferred it's use over 'FOSS'.

It's a good question when you realise you don't know the answer!

Thanks for the links @danielst and @bjoern !