This pertains to SNMP tests such as on a router.
The "grouping" element is the label under which interface tests are grouped (for organization and to expand/collapse) in a Device Details vies where tests are listed. See picture.
The grouping element for SNMP tests is "auto" generated when a (could be any one of many - for instance an interface utilization test) interface test is first created. Subsequent tests created for that interface (such as say a Traffic In test) then is automatically grouped under the appropriate grouping element. The grouping element is derived from a combination of the test name - which in turn is derived from the interface description set on the device - and the test OID.