The Requirements Traceability Matrix (RTM) is a template spreadsheet that software developers, IT Business Analysts and Testers can use to define and track the life of a requirement. This document maps requirements for design, implementation, and test cases. The purpose of the Requirements Traceability Matrix is to help users trace each requirement and monitor changes made to a particular requirement.
The Requirements Traceability Matrix (RTM) is usually developed in concurrence with the initial list of requirements during the Requirements Analysis phase while documenting the Business Requirements Document (BRD). As the Design Specifications and Test Protocols are developed, the traceability matrix is updated to include the updated documents. Ideally, requirements should be traced to the specific test step in the testing protocol in which they are tested.
RTM as explained by Karl Wiegers: