A requirements traceability matrix (RTM) is a tool used in project management to ensure that all requirements for a project are accounted for and tracked throughout the project lifecycle. It is a matrix that shows the relationships between the different requirements for a project, and is used to trace the requirements from their origin to their implementation in the final product or solution. It is an important tool for ensuring that all requirements for a project are properly identified, documented, and tracked, and helps to ensure that the final product or solution meets the needs of the business or customer.