A more thorough explanation:

A continuation-in-part is a type of patent application that is filed by the same applicant during the pendency of an earlier application. It repeats a substantial part of the earlier application but adds to or subtracts from the claims. This type of application contains new technical descriptions from the inventor or reflects improvements made since the parent application was filed.

For example, if an inventor filed a patent application for a new type of car engine and later discovered an improvement to the engine, they could file a continuation-in-part application to describe and claim the improvement.

A claim in a continuation-in-part application is entitled to the benefit of the parent application's filing date if the claimed subject matter is the same, but new matter takes the filing date of the continuation-in-part application. This means that any claims in the continuation-in-part application that are the same as the parent application can use the earlier filing date, but any new claims will have a later filing date.

Continuation-in-part applications are usually filed to describe and claim later-discovered improvements to an invention, or to distinguish the invention from some prior-art reference. They are also known as continuation-in-part application, continuation application, continuing application, or file-wrapper continuation application.