The sweet truffle is a bit size confection made out of chocolate with chocolate inside (ganache). At least in my book they are all chocolate through and through. Some people will eat a truffle that has flavor creams in the middle and the stores sell them a truffles but I strongly believe that they should be chocolate through and through (with perhaps an occasional "flavored" chocolate filling.)
Turns out the European truffle is a imperfectly shaped chocolate ball rolled in cocoa powder or nuts. These resemble the fungus thus the name. Just like their namesakes, chocolate truffles have come to connote luxury and indulgence. A sensual pleasure well worth the price.