When is a wine really dry?  What is dry?  

There are dry climates, meaning that humidity is relatively low.

There are dry senses of humor.  Steven Wright has one.  Jeff Dunham does not.  Incidentally, Jeff Dunham doesn't have humor, either.

In wine, however (or beer, or spirits), "dry" refers to the absence of residual sugar in a drink.  To simplify, take the classic kid-making-Kool-Aid example:  to make a batch of delicious Kool-Aid, one combines the tiny packet of purple with 2 heaping cups of sugar and 2 quarts of water.  However, as I kid, I didn't realize that anything beyond the packet of purple and water was needed.  I ended up with purple-colored acid water.  Sure, I tried to sell it as "Kool-Aid Dry", but my 5-year-old friends had really unsophisticated palates...

...hillbillies.

So far, so good?  A wine without the presence of residual sugar (meaning actual fruit sugar left over in the wine that was not converted to carbon dioxide and alcohol by yeast during fermentation; or, sugar added to a dry wine after fermentation, as in the case of süssreserve) is "dry".  Otherwise, a wine with sugar present might be called "off-dry" or "sweet" or "Arbor Mist".*

Yet, in my very important day-to-day business dealings, I have many folks tell me that dry wines taste sweet, and many others are extraordinarily dry.  In the case of the former, a wine with a great deal of ripe fruit flavor can be perceived by our palates as being sweet.  However, said fruit-forward wine may contain little or no residual sugar, therefore- technically- it's dry.  'Tis a very difficult concept to explain without making someone feel like a dumb-ass or coming off like a jerk-ass.  But a very fair observation for any fledgling wine lover to make.

An extraordinarily common misconception is when a person thinks a wine is "dry", when, in fact, it is "drying".  Remember:  in wine terms, "dry" is the absence of sugar.  But when drinking a wine makes one's mouth lockjaw like a rusty nail to the foot, that is a product of tannin.  That fuzzy feeling in your mouth after drinking a young Cabernet Sauvignon?  Tannin.  

Tannins are basically astringent compounds that exist in grape seeds, skins, and stems, and in wood (like oak barrels).  They add structure to wines, pleasant bitterness, and lend to color.  However, tannins bind to proteins and precipitate.  As human saliva contains proteins, these tannic phenolic compounds basically bind to our saliva, giving the sensation of drying out our mouths.  So, if you are someone who is insecure about your "wine speak" (and 99% of it is B.S. anyway, so don't be uptight), the formula is simple:

Refer to a wine in which you sense no presence of sugar as "dry"

Refer to a wine which dries your mouth out as "tannic"

Of course, anyone who gives you a hard time about using the proper terminology when discussing wine should get a Champagne cork to the nuts.  But, I understand it's import for people to feel comfortable with their wine, and this is a nice, valuable tidbit to know.

Another tidbit:  don't feed your cat Arbor Mist.

*I don't mean for this comment to suggest that sweet wines are of poor quality.  Some of the finest (and most expensive) wines in the world are quite sweet.