Domestic Sherry-style wines are made in the United States and are usually fortified wines aged in similar conditions as Spanish Sherries. Sherry is a fortified wine made in several countries, most famously from the Xerez district if Spain ( the word "sherry" itself is a derivation of the word Xerez). There are several different types ranging from very dry and light (Fino) to very sweet and rich (Cream, Moscatel).
Most are made with the fortification - increasing the alcoholic level - by adding neutral grape sprits after fermentation. This increases the alcohol from 13% or 14% up to 18% to 20%. Sherry is aged in casks for anywhere from two to eight years; the system of aging in casks is the solera system where old and new barrels are used. When wine evaporated from the old barrels, wine from the new barrels is added to top up the old barrels.
While Sherry is most commonly associated with Spain, it has become a generic term and can be produced (often via different methods) in the US and other countries.