A more thorough explanation:

Definition: Additional claims after allowance refer to claims that are submitted for the first time by amendment after the U.S. Patent and Trademark Office has informed the applicant of the patent application's allowance. Once a notice of allowance has been issued, the applicant may not by right submit additional claims. However, in some circumstances, such as when the applicant seeks to add only dependent claims, the supervisory examiner has the authority to enter an amendment containing additional claims after allowance but on or before the date when the issue fee is paid.

Example: Let's say that John has applied for a patent for his invention and has received a notice of allowance from the U.S. Patent and Trademark Office. However, he realizes that he wants to add some additional claims to his patent application. In this case, John can request to add only dependent claims, and the supervisory examiner may allow him to do so before the issue fee is paid.

Explanation: This example illustrates how an applicant can request to add additional claims after receiving a notice of allowance. However, this is only possible in certain circumstances, such as when the applicant seeks to add only dependent claims, and the supervisory examiner has the authority to allow it.