search by lattitude/longitude

How I understand it, you want to be able to enter the latitude/longitude inside the search box (at http://osm.org) and get brought there. At the moment this is not possible. You can do this by typing your coordinates into the search box, like this: "50.6950 13.3829", where 50.6950 is your latitude and 13.3829 is your longitude. Another way is to type them directly inside the URL:

http://osm.org/#map='zoomlevel'/'latitude'/'longitude'

Replace the stuff inside the apostrophes with the following:

• 'zoomlevel' = something between 0 (no zoom) and 19 (highest zoom)
• 'latitude' = the latitude you want
• 'longitude' = the longitude you want

If this is not what you want, you have to explain your question better.

Edit: Thanks for Tordanik for pointing out that you can actually search for latitute/longitude inside the search box.

I think the user refers to 'reverse geocoding' that returns the closest road/address to a geopoint. This is supported e.g. by nominatim