Alpine region is one above the tree line. [Wikipedia]
A hill is a landform that extends above the surrounding terrain, in a limited area. Hills often have a distinct summit, although in areas with scarp/dip topography a hill may refer to a particular section of scarp slope without a well-defined summit (e.g. Box Hill). A hillock is a small hill. [Wikipedia]
A slope formed at the base of a steeper slope, made of fallen and disintegrated materials.
The shady (usually poleward) side of a mountain.