Welcome to Nominatim
Nominatim is a search engine for OpenStreetMap data. This is the debugging interface. You may search for a name or address(forward search) or look up data by its geographic coordinate(reverse search). Each result comes with a link to a details page where you can inspect what data about the object is saved in the database and investigate how the address of the object has been computed.
For more information visit the Nominatim wiki page.