the trait element provides a generalized approach to set named properties on any test-case or group of test-cases, using a name/value pair.

In the example below, the test is given a severity value of high and a debug-tip of run in SSMS.

<test name="...">
  <trait name="severity">high</trait>
  <trait name="debug-tip">run in SSMS</trait>

These traits are not used for any purpose by the framework itself but are displayed in the report generated by NUnit and available in the Test Properties dialog of the UI.