Definition:
Round-trip engineering (RTE) is a functionality of software development tools that synchronizes two or more related software artifacts, such as, source code, models, configuration files, and even documentation. The need for round-trip engineering arises when the same information is present in multiple artifacts and therefore an inconsistency may occur if not all artifacts are consistently updated to reflect a given change. For example, some piece of information was added to/changed in only one artifact and, as a result, it became missing in/inconsistent with the other artifacts.
Further Reading:
Book: The Unified modeling Language user guide by Grady Booch, James Rumbaugh and Ivar Jacobson