X is located along the side of the mountain where a glacier is eroding the landscape to eventually create a deep, steep-sided hollow known as a cirque (B).

An arete(A) is a knife edged ridge between two cirques.

A truncated spur (C) is a triangular face on the vertical walls of the U-shaped valley.

Medial moraine (D) occurs when two glaciers merge together into one main valley and their lateral moraines combine to form a strip of erosional debris down the middle of the newly formed combined glacier.