A more thorough explanation:

A patent-application amendment is a change made to a patent application, usually to narrow or eliminate some claims in response to an examiner's rejection. There are different types of amendments that can be made at different stages of the application process:

• Amendment after allowance: An amendment submitted to the U.S. Patent and Trademark Office after the application has been approved. This type of amendment is usually made to correct formal matters or address prior art.
• Amendment after appeal: An amendment made after an appeal is taken from a patent application's final rejection. This type of amendment is not made as a matter of right but is frequently allowed if it puts the case in better form for consideration on appeal.
• Amendment after final action: An amendment made after final rejection of the patent application. This type of amendment may drop claims but not add them, and may make changes in form but not raise new issues for the examiner.
• Amendment after payment of issue fee: An amendment made by the applicant after the application has been allowed and the issue fee paid. This type of amendment is not made as a matter of right and requires a petition to the Commissioner showing good and sufficient reasons why the amendment was not presented earlier.
• Preliminary amendment: An amendment filed before the U.S. Patent and Trademark Office issues an office action on a patent application. This type of amendment is not considered part of the original disclosure.

For example, an applicant may submit an amendment after allowance to correct a typographical error in the specification or to add a citation to prior art that was not previously considered. Another example is an amendment after final action that drops a claim that was rejected by the examiner but leaves the remaining claims intact.