Beer
Beer is an alcoholic beverage usually made from malted cereal grain (such as barley), flavored with hops, and brewed by slow fermentation.
For purposes of distillation, beer is another name for wort. Beer made for the purpose of distillation is in general not boiled and does not contain hops. It would be considered unpalatable by any drinker of commercial beer.
Mashing wort for the purpose of distillation is different than for beer to be drunk. Distillers aim to maximize the fermentable sugars from the source materials. Unfermentable sugars left in a wort will not carry over or flavor the distillate. It is considered to be a waste. The mashing process for distillers will normally be a single step with a saccharification rest at a low temp (140-145f) to maximize fermentable sugars.
Distillers tend to distill their beer quickly after fermentation has stopped. As there is less need to worry about infections beer is not normally boiled (pasturized). It also is considered to be wasteful. In some styles of brewing infections of certain bacteria is encouraged. Common strains include Lactobacillus and Acetobacter.