A more thorough explanation:

Definition: Double use refers to the application or employment of a known principle or process to a new use without leading to a new result or product. It is a type of patent infringement where an existing invention is used for a different purpose without creating a new product.

Example: A company has a patent for a machine that makes paper cups. Another company uses the same machine to make paper plates without making any changes to the machine. This is an example of double use.

This example illustrates that the second company is using an existing invention for a different purpose without creating a new product. This is not allowed under patent law as it infringes on the original patent holder's rights.