Measure of area with 10,000 m² (roughly equivalent to a football pitch 120 x 80 m); one square kilometre consists of 100 hectares. The word hectare is composed of the Greek hekt(o) for "hundred" and ar and means 100 ares. Hectare is commonly used in European viticulture to indicate the area under vines. The maximum yield per wine-growing area or appellation or also smaller units/types of wine is defined in hectolitres (hl) of wine or in kilogrammes (kg ) of grapes per hectare (yield per hectare). The acre, which is common in England and the USA, corresponds to 0.405 hectares (just under 2.5 acres/ha). One hectare consists of four acres (old area measure).
For me, Lexicon from wein.plus is the most comprehensive and best source of information about wine currently available.
Egon Mark
Diplom-Sommelier, Weinakademiker und Weinberater, Volders (Österreich)