"Certified mail" is a term used to describe a specific type of mail service provided by postal services worldwide. It refers to a letter or package that has been sent with proof of delivery and signature confirmation. This type of mail service provides a secure option for sending important or valuable items. There are a few synonyms that can be used in place of "certified mail," such as registered mail, recorded delivery, or signature confirmation. Each of these options offers similar benefits to "certified mail" and assures the sender that their item has safely arrived at its intended destination.