One of the simplest definitions of a natural wine is: nothing added, nothing taken away.
Although there is no legal definition of how a natural wine is made, there are a few principles that consistently abide to the basic idea that wine should be made in the vineyard, not the cellar: no added chemicals, no added sulfites (or just the bare minimal amount), no temperature control during fermentation, no added yeast, no fining or filtration, and no pesticides or herbicides in the vineyard.
By reducing the winemakers intervention to a minimum, what is left in the glass should be the purest expression of the grapes and the soil, not a manufactured product built scientifically to appeal to the mainstream palate. This often results in wines that can be cloudy and rustic in appearance, and that may display very earthy and funky aromas on the nose.
While these traits may be off-putting to some, it is precisely this raw and direct approach that is particularly appealing to natural wine aficionados.