A more thorough explanation:

A nonassertion letter is a written declaration by a patent holder stating that they do not intend to enforce their right to exclude others from practicing certain claims of their patent. The patentee may choose to waive this right entirely or specify a time limit for the waiver.

For example, if a company holds a patent for a certain technology but decides not to enforce it against a competitor, they may issue a nonassertion letter to the competitor stating that they will not take legal action against them for using the technology.

This type of letter can help to avoid costly and time-consuming patent litigation and can also promote collaboration and innovation in the industry.