If you are a COLLECTOR, then beware of arsenal refinished guns! Well, maybe I'm being a little harsh - let me explain.. Ask who it was refinished by. As Jeff said, it is SUPPOSED to mean that a government arsenal reworked it back into a condition that is good enough to give to the troops.
HOWEVER, there are some C&R guns that were "arsenal refinished" by a private company that bought some crappy guns and tried to clean them up. A good example of this is some German K98 mauser rifles that were captured by the USSR during WWII and later "refinished" and sent to the US. Another example is the "unissued" Enfield No1 MkIII rifles, which were actually put together from scrap parts by a private company. These guns have a SUBSTANTIAL loss of value to collectors!
If you are looking at a particular gun, we might be able to give you a better idea about it. For instance, many US battle rifles that are on the market today were arsenal refinished by a US government armory. This is okay and should be expected. However, as time goes by, we are seeing more and more guns that were privately refinished by import companies. These guns are worth much less.
I hope my long-windedness was of some help,
Gino