I've only encountered the term on MN, and always assumed it meant you take the exams online instead of as a written exam, because that's the rule when you stick an 'i' infront of any other word!
Silly Belle 
I've just realised I'm dead wrong. I tried Googling, but it just left me confused - I am the mother of primary school aged DC, and my GCSEs were taken a looong time ago.
So what's the difference between bog-standard GCSEs and IGCSE? No reasons why I want to know, except I'm very curious to know if technology is involved. 