this is a Abbreviation for word "for your information" mostly this is use in email trails when you are going to send some files,instruction and information information. cowboy...

Funnily enough it has creeped over to the spoken language as well, where it has become 'net savvy' to drop it every now and then. Things like, "Don't worry about it, it's just an FYI" - means, that piece of information is simply that, information, it doesnt require any follow-up or anything. etc

If you ever want to use it, it comes right before the information you'll give. "FYI, you'll find the milk on the third shelf." You could add it at the end of the sentence for a slightly condescending tone: "You'll find the milk on the third shelf, FYI (='as if you didn't already know')." I don't actually hear this commonly spoken, is it pronounced as an acronym? "Eff-why-eye?" I'd expect IT folk to use it.