A more thorough explanation:

Complementary goods are products that are typically used together. For example, pancake syrup and pancake mix are complementary goods because they are often used together. Another example is 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. This means that if a company has a trademark for pancake syrup, another company cannot use a similar trademark for pancake mix because it may confuse consumers.

The patent-misuse doctrine may provide a defense in an infringement suit if the plaintiff has used its patent rights to gain market control over unpatented complementary goods. This means that if a company has a patent for motion-picture projectors, it cannot use its patent to gain control over the film market.

Overall, complementary goods are products that are used together and may be subject to trademark and patent laws.

• Hot dogs and hot dog buns
• Toothbrushes and toothpaste
• Computer hardware and software

These examples illustrate complementary goods because they are products that are often used together. For example, hot dogs and hot dog buns are complementary goods because they are typically used together when making a hot dog. Similarly, toothbrushes and toothpaste are complementary goods because they are used together when brushing teeth.