Relative to Aust, grey's obviously any product that's purchased not through the official importer channels.
But consider the following scenario?
1. Buying a US model camera online from BH (located in US) but sent directly to Aust.
2. Buying a US model camera online from BH but sent to a US address then either forwarded by post or in person to Aust.
3. Buying any products in the country that it was officially imported to, whilst in that country. Eg. Buying a HK product while in HK.
As far as I know, whatever's considered a grey product won't be repaired at all by the official manufacturer in or out of warranty.
But if it's not considered grey but bought in a different country, does warranty repairs get sorted in whichever country you're in or sent back to country of origin. Does this differ based on the product eg. I've heard optical products eg. Lenses are treated differently to digital products eg. DSLRs.