From OpenStreetMap Wiki
|a name prefix|
|Used on these elements|
|Status: in use|
|Tools for this tag|
This is used for 2 purposes:
- street names: A directional prefix/suffix that is not part of the actual street name but part of addresses. Currently used in the US. See proposal. On highway=* only. Renderers should certainly ignore these prefixes and suffixes.
- categorization: The name of the administrative level (e.g. "town", not the name of the town). Currently used in Eastern Europe and Germany. See this proposal for a summary of alternative tags. Renderers should include these prefixes and suffixes when rendering names. For most other applications, the prefixes and suffixes should be ignored.
The tags are in use in some countries, although the proposal for (1) has been abandoned, and there has never been a proposal for (2).