From OpenStreetMap Wiki
|Secondary house numbers known as "číslo orientační" in the Czech Republic.|
|Used on these elements|
|Status: de facto|
|Tools for this tag|
Even though this key was not approved officially, it was accepted as a part of widely used, official address tagging system for the Czech Republic.
Usage in the Czech Republic
For instructions on tagging addresses in the Czech Republic see Czech address system(cs).