A more thorough explanation:

A perfecting amendment is a formal revision or addition proposed or made to a statute, constitution, pleading, order, or other instrument. It is a change made by addition, deletion, or correction, especially an alteration in wording. The process of making such a revision is also called an amendment.

For example, an amendment to a constitution can be made to change a law or add a new one. A nunc pro tunc amendment is given retroactive effect, usually by court order. An amendment on the court's own motion is a change to a pleading or other document by the judge without a motion from a party.

In parliamentary law, a perfecting amendment is a motion that changes another motion's wording by striking out text, inserting or adding text, or substituting text. An amendment by adding places new wording at the end of a motion or of a paragraph or other readily divisible part within a motion. An amendment by inserting places new wording within or around a motion's current wording. An amendment by striking out removes wording from a motion's current wording. An amendment by striking out and inserting removes wording and replaces it with alternative wording.

Overall, a perfecting amendment is a way to improve or correct a document or motion by making changes to its wording.