Taken from one of my favorite websites called Wise Geek
Retsina is a unique wine product made almost exclusively in Greece. It is made with a base of white or rosé wine that is flavored with pine resin. The wine is quite pungent, and not to everyone's taste. However, the Greeks have been making and drinking it for over three thousand years, and people often find it more enjoyable when it is paired with Greek foods. Retsina also varies widely in quality, and an inferior product can taste suspiciously like turpentine. Consulting the staff at a Greek wine store may be the best way to find a good wine.
The name for retsina is derived from a Latin word, resina. The official explanation for the drink has it roots in early wine making practices. Lacking airtight containers for fermentation, many early white wines soured as a result of exposure to oxygen. To stave off this problem, wine makers covered their wine jugs in pine pitch, the same material used to waterproof boats. The pitch effectively sealed the containers so that the wine did not spoil, and consumers developed a taste for the resulting resinous wine.