What, when signed by all parties to a sales contract, changes the original terms of the contract?

An amendment is a formal change made to the original terms of a contract that is agreed upon by all parties involved. It modifies, adds to, or clarifies the terms without needing to create a whole new contract. This is crucial because it maintains the original agreement's framework while allowing for necessary adjustments to be made, which can be due to various reasons such as changes in price, timelines, or other specific terms.

An addendum, while also a way to add terms, is often considered an addition to the existing document rather than a direct change to terms already established. Annexation refers to the physical attachment of something or an expansion of land, and appurtenance pertains to something that is a supplementary or auxiliary part of a property, typically in relation to real estate, such as a garage or garden, and does not specifically deal with contract terms.