Au sec (pron. “oh sek”) is a French phrase meaning “dry.” 

“au Sec” in the Kitchen:
Like nappe, au sec is used in the classic French culinary tradition (even by English speaking chefs) to reference a specific point in the cooking process.  However, in the kitchen, it doesn’t actually mean dry, but rather “almost dry”…because when pans get completely dry they tend to burn things.

Au sec shows up in classic recipes where a liquid is being reduced down to the point where it is almost completely evaporated.  Liquids commonly reduced au sec are white or red wine, chicken stock, veal stock, or vinegars.  Au sec is an important phase, culinarily speaking, because at this point the liquid doesn’t really add volume or moisture to a dish, but is still present as flavor.  You’ll see it in some sauce recipes, and often in risotto recipes, referring to the reduction of the white wine used to deglaze the pan (how to make risotto).

“Sec” on Wine Labels:
Sec also shows up on French wine labels where it also means dry (as in “not sweet”). 

On sparkling wines, “sec” refers to a whole range of sweetness levels that are sweeter than the “brut”s but not actually in the ”sweet” category (which actually refers to the very sweetest sparkling wines):

“extra-sec” means extra-dry
“sec” is in the middle
“demi-sec” is the sweetest wine NOT in the “sweet” category  (a little confusing…but a lot of wine terminology can be).