What do these "OG" and "RDF" numbers mean? I recently got a "Gnarly Oak" craft brew package. Three 22 oz beers and a glass. However, on the beers are some abbreviations and numbers I don't understand. they all have a 5.5% ABV, and I get the IBU and color numbers but what are the rest? The numbers and abbr's are below:


  
  Winter Bock - 15 OG, 62.5 RDF - light, tasty, ever so slightly bitter
  Hazelnut Dark - 15 OG, 60.4 RDF - nice bitter red with slightly sweet aftertaste
  Chocolate Stout - 14.8 OG, 66.8 RDF - very sweet with hints of chocolate and malt
  


EDIT
In light of the answers so far, I should say I have brewed my own, and if OG is original gravity, it doesn't fit with the scale I know of. if 15 OG ~= 1.015, it doesn't match what that would give in final ABV. Is this OG on a different scale I haven't seen
From the figures you posted,

OG - "Original Gravity". When measured with a hydrometer, it measures the density relative to water. E.g. 1.010 is 1% heavier than water. The units here are degrees Plato (&deg;P), which describe the amount of dissolved sugars. Here, 15 means 15% dissolved sugar. This means the beer (or more correctly, the wort) contained 15% sugar before fermentation started.

RDF - The real degree of fermentation. This is in contrast to the Apparent Degree of Fermentation, which is (OG-FG)/OG. When the final gravity is measured using hydrometer, the alcohol in the beer, being less dense than water (SG. 0.789) causes the gravity to appear lower, so it looks as though the yeast has fermented more sugar than it actually has. The Real degree of Fermentation takes the alcohol into account and computes the actual amount of sugars fermented. This tells you the how much of the original sugar was fermented (as a percentage). 

So, what does this mean in practice?


  Winter Bock - 15 OG, 62.5 RDF - light, tasty, ever so slightly bitter


This has an average RDF for a beer that size, so it will be somewhat malty, but not cloying.


  Hazelnut Dark - 15 OG, 60.4 RDF - nice bitter red with slightly sweet aftertaste


This has more dissolved sugars in it compared to the Bock, so you'd expect it to be a thicker mouthfeel and slightly more sweet, although you may not taste the sweetness if it's offset by roasted malts.


  Chocolate Stout - 14.8 OG, 66.8 RDF - very sweet with hints of chocolate and malt


Being the driest of all the beers, yet the taste description is given as very sweet. This shows that knowing the residual sugars doesn't tell you the sweetness, simply because there are different kinds of residual sugar. For example, dextrins create body, but have relatively little taste, so would taste not as sweet as a beer containing a lot of residual maltose or glucose.