The Terrain Collider implements a collisionA collision occurs when the physics engine detects that the colliders of two GameObjects make contact or overlap, when at least one has a rigidbody component and is in motion. More info
See in Glossary surface with the same shape as the TerrainThe landscape in your scene. A Terrain GameObject adds a large flat plane to your scene and you can use the Terrain’s Inspector window to create a detailed landscape. More info
See in Glossary object it is attached to.
|MaterialAn asset that defines how a surface should be rendered, by including references to the Textures it uses, tiling information, Color tints and more. The available options for a Material depend on which Shader the Material is using. More info
See in Glossary
|Reference to the Physics Material that determines how this ColliderAn invisible shape that is used to handle physical collisions for an object. A collider doesn’t need to be exactly the same shape as the object’s mesh - a rough approximation is often more efficient and indistinguishable in gameplay. More info
See in Glossary interacts with others.
|Terrain Data||The terrain data.|
|Enable Tree Colliders||When selected Tree Colliders will be enabled.|
You should note that versions of Unity before 5.0 had a Smooth Sphere Collisions property for the Terrain Collider in order to improve interactions between terrains and spheres. This property is now obsolete since the smooth interaction is standard behaviour for the physics engineA system that simulates aspects of physical systems so that objects can accelerate correctly and be affected by collisions, gravity and other forces. More info
See in Glossary and there is no particular advantage in switching it off.