Final answer:
The unique number assigned to each service line on a claim by the sender is called a Reference, just as DOIs and URLs serve as unique identifiers in academic publishing and online resource location.
Step-by-step explanation:
The unique number assigned by the sender to each service line on a claim is known as a Reference. This reference number serves as a crucial identifier that allows both the sender and recipient to track and manage claims effectively. The importance of this number is similar to other unique identifiers used in various systems for precise referencing, such as a DOI (Digital Object Identifier) for academic articles or a URL (Uniform Resource Locator) for locating online resources.