The tags railway=razed, railway=dismantled and railway=historic are used to tag a former railway, where mostly all evidence of the line has been removed. None of those Tags are considered a standard by a majority of mappers, some even consider them to differ slightly in what they mean.
Most mappers follow a basic Good practice#Map what's on the ground principle, and would therefore regard the mapping of non-existant railways as incorrect data to be placing in the OpenStreetMap database. On the wiki this is discussed at Talk:Railways#Abandoned railways where all evidence has been removed and multiple times on mailing lists, see for example 
Of the tags below, only railway=razed is rendered on OpenRailwayMap.
Overall, mapping such features is acceptable where some remains like embankments, remains of bridges etc remain. Where it was replaced by new buildings and roads the mapping of such features becomes out of scope for OpenStreetMap.
|The Old-Wiki-Definition: If it is impossible to guess the former route use railway=dismantled instead. 1||The Old-Wiki-Definition: Is a key to tag a former railway, where all evidence of the line has been removed. It may have been replaced by new buildings and roads that don't refer to the old alignment, or may have been returned to farmland. 2||A Wiki-Definition never existed. But there are historic=railway (On Page Historic) or historic=railway (on History-Map).|
There are many.
- Seltsame Tags für Verkehrswege in the german Section of the OSM-Forum
General historic mapping: