A chocolate chip cookie

In the United States and Canada, a cookie (or cooky) is a small, round, flat cake. In most English-speaking countries outside North America, the most common word for this is biscuit; in many regions both terms are used, while in others the two words have different meanings—a cookie is a plain bun in Scotland, while in the United States a biscuit is a kind of quick bread not unlike a scone.

A cookie cake is a large cookie that can be decorated with icing similar to other cakes.

Cookies can be baked until crisp or just long enough that they remain soft. Depending on the type of cookie, some cookies are not cooked at all. Cookies are made in a wide variety of styles, using an array of ingredients including sugars, spices, chocolate, butter, peanut butter, nuts or dried fruits. The softness of the cookie may depend on how long it is baked.

A general theory of cookies may be formulated this way. Despite their descent from cakes and other sweetened breads, the cookie in almost all its forms has abandoned water as a medium for cohesion.