A traceability matrix is a document, which is normally in tabular format. That correlates any two baseline documents and ensures completeness of the relationship. Relationship of each item of documents will be many to many.
The usage of this document is the most popular in Software development industries to map other documents with baseline software requirement document so it is called Requirement Traceability Matrix document. In which all other documents like High Level, Low Level design documents, Test Cases, Unit Test document IDs are mapped with baseline requirement document IDs to ensure that every requirements are documented, developed, tested and delivered.
I have created Requirement Traceability Matrix for Software Development companies, which covers relationship among all artifacts. Many people are thinking that to maintain such document is time consuming activity but when we use and maintain it properly then that becomes really helpful to team members and project stakeholders.
Project Leads can customize the document as per their requirements like if project leads are maintaining Application design document instead of High level or Low level design documents then they can replace High Level and Low Level design documents Section IDs columns with Application Design document Sections ID even they can remove the columns as well like the application does not have any user manual then Project lead can remove it from Matrix sheet. I strongly recommend that all project leads should maintain the document and project managers should ensure that in the interest of Project.