What defines cooking wine?

At least in germany "cooking wine" is more a reference to a cheap wine that just does not taste good if drunken (or is of a low percieved quality). For example a cheap lambrusco, which you get if you order a few pizzas at your local pizzaria, is considered "cooking wine" in germany.

Cooking wine has added salt so it is unpalatable to drink and legal to be sold in a store that doesn't have a liquor license in states requiring that.

As my answer is quite long, it was suggested to add a summary up front. Here are the main points along with a little more info.

• In the US, commercial cooking wines found in the grocery store, usually on the aisle with vinegar products, contain salt and other preservatives. The main reason for this is stability, giving the products a longer shelf life after opening. Other reasons may include taxation and regulations. The same is true of cooking sake.

• In the US, drinking wines that are usually cheap or of lesser quality may be considered cooking wines. Sources state that the difference between these wines and wines that one would prefer to drink is quality. Also, these wines may contain a higher amount of alcohol than those labeled as cooking wines. Due to a higher alcohol content, one may achieve more complex or deeper flavors.

• Based on other answers and comments, salted wine doesn't seem to be common in many other countries.

• Some wines that are considered to be cooking wines, such as Shaoxing (which is a Chinese cooking wine) seem to be quite easy to find with no salt.

As per my comments, I don't feel that there is just one definition or that one blanket statement gives a full and complete answer to this question. Thus, my quest to provide an answer that covers more ground.

Cooking wine, depending on location can mean several different things. As noted in the answer above, it is different in Germany than in the US. Even in the US, there is much conflicting information, as well as many different products considered to be cooking wine.

From Wine Folly, which is written by a certified sommelier:

Just so you know, the major difference between wines sold as cooking wines vs. regular drinking wines is quality. If anything, cooking with a regular drinking wine will give you a better tasting dish because the quality is much higher.

From leaf article: Differences Between Cooking Wine and Drinking Wine:

Although cooking wine and wine for drinking share some added ingredients, they differ in two main ways:

• Cooking wine contains salt, which gives foods an overly salty or bitter flavor.
• Drinking wine contains more alcohol, which reacts with both heat and certain foods to add complex, deep and new flavors to a dish.

As for why salt or other additives are used, taxes and regulations could be a factor, but the most important factor is that it lengthens the shelf life after the bottle has been opened. Also from leaf:

The added salt in cooking wine gives it a longer shelf life than drinking wine. Cooking wines come with "use by" dates, but are typically good at room temperature for 3 to 4 months. Drinking wine stays fresh for drinking for about 5 days in the refrigerator, but will still work for cooking for 2 months.

From Holland House, either the largest (or one of the largest) manufacturer of 'grocery store cooking wines' in the US:

1. Q: What is cooking wine?

A: Holland House Cooking Wine is wine MADE for cooking. Holland House uses premium quality wine stock and has a perfectly balanced taste and aroma. The salt that is added makes it stable in your pantry. This gives you a consistency of flavor you can depend on from the first time you open it to the last drop. Cooking wine is used as an ingredient; it is not meant to be consumed as a beverage.

(Emphasis mine.)

So, to sum up, there are many different products or 'wines' considered to be cooking wines. There is not just one single answer to the definition of a cooking wine. It totally depends on geographical location and which 'wine' is in question. Is it a commercial cooking wine? Is it a poor or lesser quality 'drinking wine' that is typically considered to be a cooking wine? There are too many variables to sum it up in one brief sentence.

Other answers have focussed on wine, I'll focus on sake.

"Cooking sake" is a rice alcohol. Sake doesn't have any spices added to it. Cooking sake is just a lower" quality sake. It will also likely have other additives like salt and anti-oxidants to stabilise the alcohol. Cooking sake is expected to last in a usable condition for longer than a quality drinking sake. I don't doubt that some cooking sake is made by diluting cheap sake with water and grain alcohol, to reach a certain price point.

There is another alcoholic product that may be labelled as "cooking sake". Mirin is a sweet alcohol exclusively for cooking. It has syrup added to it after fermentation. Its used for example in teriyaki sauces.

As noted in other answers, in the US "cooking wine" is nearly always salted, elsewhere it normally refers to a low-quality wine, for example, one made with sugar and grape concentrate.