Rye whiskey can refer to either of two types of whiskey: 1) American rye whiskey, which must be distilled from at least 51 percent rye

Rye

Rye is a grass grown extensively as a grain and as a forage crop. It is a member of the wheat tribe and is closely related to barley and wheat. Rye grain is used for flour, rye bread, rye beer, some whiskeys, some vodkas, and animal fodder...

; 2) Canadian whisky

Canadian whisky

Canadian whisky is a type of whisky produced in Canada. Most Canadian whiskies are blended multi-grain liquors containing a large percentage of corn spirits, and are typically lighter and smoother than other whisky styles...

, which is often referred to (and labelled as) rye whisky for historical reasons, although it may or may not actually include any rye in its production process.
In the United States

United States

The United States of America is a federal constitutional republic comprising fifty states and a federal district...

, "rye whiskey" is, by law, made from a mash

Mashing

In brewing and distilling, mashing is the process of combining a mix of milled grain , known as the "grain bill", and water, known as "liquor", and heating this mixture...

 of at least 51 percent rye. (The other ingredients of the mash are usually corn

Maize

Maize known in many English-speaking countries as corn or mielie/mealie, is a grain domesticated by indigenous peoples in Mesoamerica in prehistoric times. The leafy stalk produces ears which contain seeds called kernels. Though technically a grain, maize kernels are used in cooking as a vegetable...

 and malted barley

Barley

Barley is a major cereal grain, a member of the grass family. It serves as a major animal fodder, as a base malt for beer and certain distilled beverages, and as a component of various health foods...

.) It is distilled to no more than 160 (U.S.) proof (80% abv

Alcohol by volume

Alcohol by volume is a standard measure of how much alcohol is contained in an alcoholic beverage .The ABV standard is used worldwide....

), and aged in charred, new oak

Oak

An oak is a tree or shrub in the genus Quercus , of which about 600 species exist. "Oak" may also appear in the names of species in related genera, notably Lithocarpus...

 barrel

Barrel

A barrel or cask is a hollow cylindrical container, traditionally made of vertical wooden staves and bound by wooden or metal hoops. Traditionally, the barrel was a standard size of measure referring to a set capacity or weight of a given commodity. A small barrel is called a keg.For example, a...

s.