Retsina is a Greek drink that accompanies many meals in the Greek tavernas. It is a type of wine, of a bit lower quality, that makes it is much cheaper than wine. When you visit Greece and Thessaloniki you will see many tables around you in the taverns having this drink. It is the drink of that is associated with big companies of people because it is cheap and the companies consume large quantities of alcohol.
The production of retsina has its roots in the ancient Greek times when the addition of resin (resin-primary component of retsina) aimed at a better conservation of the wine, and not only to add flavor. In Thessaloniki many restaurant also offer retsina in bulk solutions and sell it by the liter. You will also find there red and white wine served also bulk. Even if you love the expensive wine I would suggest you to try this bulk solutions. Sometimes these wines have really very good quality. For sure they will be at least of medium quality so do not hesitate to try them.