A more thorough explanation:

A notice of incomplete application is a notification sent to a patent applicant by the U.S. Patent and Trademark Office when a patent application is missing a required document or the filing fee. This notice informs the applicant that their application cannot be processed until the missing information or fee is provided.

For example, if an applicant submits a patent application without paying the required filing fee, they will receive a notice of incomplete application. The notice will inform them that their application cannot be processed until the fee is paid.

The applicant typically has two months to provide the missing information or fee, but they can request an extension by paying a surcharge.