Amendment

We'll assume you're an expert on the U.S. Constitution and, by extension, the Bill of Rights and the other amendments...you know, the first amendment (freedom of press, religion, etc.), the fifth amendment (don't talk to the police) and, of course, the twenty-third amendment (we don't have to explain that one, do we?).

The same idea behind Constitutional amendments applies to amendments in the financial world. A contract exists (like the Constitution). The parties want to change the contract ("hey, it looks like you guys forgot to guarantee free speech...let's fix that before we really get going on this government thing"). So amendments are added to the contract to enact the changes.

In business, companies can amend contracts to update information and alter terms. New prices, an updated end date, altered delivery expectations, even things like changed addresses can get worked into the original contract through amendments.