When choosing a mountain boot, it is important to determine which category of boot you will require. These categories are defined by letters: B, B/C, C, and D.
Category B and B/C
Hiking boots in this category are stiffer and stronger than Category A and A/B boots. They are made for mountainous terrain where you wear a heavy backpack and hike challenging trails.
Category C and D
This category of hiking boots are suitable for heavy hiking in the mountains, for example, a multi-day alpine hike in the Alps. The shoes have a stiff sole that is suitable for flexible crampons. The boots are also suitable for rock climbing. Using these boots for a flat walk is not recommended, as the stiff sole makes normal foot motion almost impossible on flat ground.