Vodka is a distilled spirit, made usually from grain, but it can also be made from almost any kind of food plant, including beets or potatoes.
Unlike Whiskey, which is also made from grains, vodka is not aged, and it is ready to drink as soon as distillation is complete. And unlike Gin, vodka is (normally) all but totally flavorless. In fact United States law requires that it is to be "without distinctive character, aroma, taste, or color."