There are a number of options under the Terrain Settings button in the Terrain Inspector.

Base Terrain

Pixel Error	Amount of allowable errors in the display of Terrain Geometry. This is essentially a LOD setting.
Base Map Dist.	The distance that Terrain Textures will be displayed in high-resolution.
Cast Shadows	Should terrain cast shadows?

Tree & Detail Settings

Draw	If enabled, all trees, grass, and detail meshes will be drawn.
Detail Distance	Distance from the camera that details will stop being displayed.
Tree Distance	Distance from the camera that trees will stop being displayed. The higher this is, the further-distance trees can be seen.
Billboard Start	Distance from the camera that trees will start appearing as Billboards instead of Meshes.
Fade Length	Total distance delta that trees will use to transition from Billboard orientation to Mesh orientation.
Max Mesh Trees	Total number of allowed mesh trees to be capped in the Terrain.

Wind Settings

Speed	The speed that wind blows through grass.
Size	The areas of grass that are affected by wind all at once.
Bending	Amount that grass will bend due to wind.
Grass Tint	Overall tint amount for all Grass and Detail Meshes.