From OpenStreetMap Wiki
|natural = land|
|Using this tag is discouraged, use for islands in lakes and rivers use Relations/Multipolygon, for islands in the sea use natural=coastline and place=island instead.|
|Used on these elements|
|Tools for this tag|
|This feature has been labeled as deprecated. The recommended replacement is: for islands in lakes and rivers use Relations/Multipolygon, for islands in the sea use natural=coastline and place=island. The reason is documented under Deprecated features. You are still free to continue to use or interpret this tag as you see fit since OpenStreetMap does not have "banned features".
Under no circumstances should you (semi-)automatically change "deprecated" tags to something else in the database on a large scale without conforming to the Automated Edits code of conduct.
natural=land was used for land that exists within another area, such as a lake.