Sherry is a fortified wine, made in and around the town of Jerez, Spain and hence in Spanish it is called "Vino de Jerez". Spanish producers have registered the names Jerez / Xérès / Sherry and will prosecute producers of similar wines from other places using the same name. According to Spanish law, Sherry must come from the triangular area of the province of Cádiz between Jerez, Sanlúcar de Barrameda, and El Puerto de Santa María. However the name 'Sherry' is used as a semi-generic in the United States where it must be labeled with a region of origin such as American Sherry or California Sherry. In earlier times sherry was known as sack (a rendering of the Spanish sacasolera]).
Sherry differs from other wines because of how it is treated after fermentation. After fermentation is complete, it is first fortified with brandy and then if destined to be fino style a yeast called flor is allowed to grow on top. Oloroso style is fortified to a strength where the flor cannot grow. Because the fortification takes place after fermentation, all natural sherries are dry; any sweetness is applied later.
In contrast, port wine is fortified half way through fermentation, stopping fermentation so not all the sugars are allowed to turn into alcohol and so leaving a sweet wine.