An addition to a completed written document. most commonly this is a proposed change or explanation (such as a list of goods to be included) in a contract, or some point that has been the subject of negotiation after the contract was originally proposed by one party. real property sales agreements often have addenda (plural of addendum) as the buyer and seller negotiate fine points (how payments will be made, what appliances will be included, date of transfer of title, the terms of financing by the seller and the like). although often they are not, addenda should be signed separately and attached to the original agreement so that there will be no confusion as to what is included or intended. unsigned addenda could be confused with rough drafts or unaccepted proposals or included fraudulently.