A more thorough explanation:

A declaration of incontestability is a statement made by the owner of a registered trademark after five years of registration. The statement declares that the mark has been in continuous use in commerce for at least five consecutive years since registration, has not become generic, has not had any final adverse decision to ownership, and has no pending proceeding in the U.S. Patent and Trademark Office or courts involving the mark.

The declaration of incontestability provides the mark with immunity from some legal challenges under § 15 of the Lanham Act. This means that the mark cannot be challenged on certain grounds, such as being merely descriptive or lacking distinctiveness.

After five years of registration, the owner of the trademark "Nike" submits a declaration of incontestability. The statement declares that the mark has been in continuous use in commerce for at least five consecutive years since registration, has not become generic, has not had any final adverse decision to ownership, and has no pending proceeding in the U.S. Patent and Trademark Office or courts involving the mark. This declaration provides the "Nike" mark with immunity from certain legal challenges.