What is Alcabala?

Legal Definition
The alcabala or alcavala (Spanish pronunciation: [alkaˈβala]) was a sales tax of up to fourteen percent, the most important royal tax imposed by Spain under the Antiguo Régimen. It applied in Spain and the Spanish dominions. The Duke of Alba imposed a five percent alcabala in the Netherlands, where it played an important role in the Dutch Revolt. Unlike most taxes in Spain at the time, no social classes were entirely exempt (for example, nobles and clergy had to pay the tax), although from 1491 clergy were exempt on trade that was "not for gain." Certain towns were also, at times, given exemptions.
-- Wikipedia
Legal Definition
In Spanish law. A duty of a certain per cent paid to the treasury on the sale or exchange of property.
-- Black's Law Dictionary