A more thorough explanation:

The Aunt Jemima doctrine is a principle in trademark law that states a trademark is protected not only from use on a directly competing product, but also from use on a product that is closely related in the marketplace. This is because consumers may be confused into thinking that the products come from a single source.

For example, in the case of Aunt Jemima Mills Co. v. Rigney & Co., the name used on pancake flour was later used on syrup. The issue was not whether a competitor was trying to pass off goods, but whether it was fair to let the name's second user jeopardize the goodwill built up by the first user.

Another example of complementary goods that may be protected under the Aunt Jemima doctrine are products that are typically used together, such as pancake syrup and pancake mix, or motion-picture projectors and film. Trademark law may prevent the use of a similar mark on complementary goods because consumers may be confused into thinking that the goods come from a common source.

The Aunt Jemima doctrine is important in protecting the goodwill and reputation of a trademark, and preventing confusion among consumers in the marketplace.