Definition - What does Brut mean?
"Brut" is a french word that means uncut, rough or raw. The term relates to the natural or raw state in which a champagne or sparkling wine is bottled. Brut wines are considered the driest in nature because they are treated with very little to no amount of additional sweetness in form of sugar. The term Brut can be defined as a style associated with the level of sweetness in a sparkling wine.
WineFrog explains Brut
The term Brut is applied to champagne and sparkling wines, which are quite dry (less sweet) and acidic in nature. This signature style of adding no sugar to the wine was pioneered in the mid-1900s by the well-known champagne House of Perrier-Jouët. Nowadays, champagne and sparkling wines are made in a wide variety of styles ranging from very sweet to intensely dry, with bottle labels indicating to what's inside as Brut, Extra Brut, Sec etc.