Port wine is a sweet, fortified wine produced in the Douro Valley region of northern Portugal. It is made by adding a neutral grape spirit (brandy) to the wine before fermentation is complete, which stops the fermentation process and leaves residual sugar in the wine. 

This results in a wine that is typically high in alcohol (typically around 20%) and sweetness. Port wines come in a variety of styles, including ruby, tawny, white, and late-bottled vintage (LBV), each with its own distinct flavour profile and production method. 

Ruby ports are youthful and fruity, tawny ports are aged in oak barrels and have a nutty flavour, white ports are made from white grapes and are usually consumed as aperitifs, and LBV ports are made from a single vintage and are aged for several years before bottling. Port wine is traditionally served as a dessert wine, but it can also be paired with strong cheeses or chocolate desserts.