This layer is a lot like the Wikipedia concept, where anyone can “view, edit and use geographical data in a collaborative way from anywhere on Earth.” You can see the layer in Bing Maps by clicking here.
Chris Pendleton from Microsoft explained:
People, like you and me, gather location data across the globe from a variety of sources such as recordings from GPS devices, from free satellite imagery or simply from knowing an area very well, for example because they live there. This information then gets uploaded to OpenStreetMap’s central database from where it can be further modified, corrected and enriched by anyone who notices missing facts or errors about the area.
Users can still perform searches atop of the OSM map layer. Once the OSM Maps are rendered, users will find the OSM map option listed in the map types so if you switch to Bird’s Eye or some other native Bing map types, you can easily return to the OSM map style. Of note, we are using the Mapnik map style from OSM (one of the many map styles available to open source users) to create our OSM map type. People love the details you see?