Hier kann man das nachlesen:

https://wiki.openstreetmap.org/wiki/Tag:junction=roundabout

Name tag:
Roundabout with individual name: name=Butlerstown roundabout
Only if the roundabout itself has a name, the name=* key is applied (such as John's Junction). It should not use the name of a road it connects. If the roundabout does not have an individual name, the name=* tag is not used. If there exist a postal addresses for residents located inside or around the roundabout which is different from the connecting highways, then this is usually the name of the roundabout. If the roundabout has no name, tag noname=yes.