Steps to reproduce:

1. Create new Unity project and scene;
2. Add Terrain Gameobject (GameObject -> 3D Object -> Terrain);
3. Notice that Terrain GO appeared in the Hierarchy view named as "Terrain";
4. Repeat step 2;
5. Notice that the second terrain is named exactly as the first one added (see attached actual.png screenshot).

Expected result:
All the new added terrains should have unique names to preserve consistency with adding other similar GameObjects (e.g. Cube) or with Duplicating terrains (in this case, duplicated terrain is named as "Terrain(1)" ). Also it's important not to mess the data with the naming of TerrainData files (which is also unique as well).