Originally Posted by greenthumbed
I'm sorry I guess I should have been more specific.
S.G. refers to "Specific Gravity". It's kinda like "Original Gravity" but more in general I would say. It refers to a gravity reading at any time of the ferment.
specific gravity (SG) is any reading with a hydrometer - it's what a hydrometer measures. original gravity (OG) and final gravity (FG) are both SG readings at different times - one is before fermentation, the other is after. so OG and FG are two SG readings taken at specific times. if you took a reading with your hydrometer half way through fermentation you would still be reading the brew's SG at that time (and the value would be somewhere between your OG and the FG).