Landforms and water
Zhu Shan (parent mountain)
The main mountain supporting the rear — the 'mountain behind' of the siting rule.

The parent mountain rises directly behind the site and is held to pass qi down to it; it occupies the tortoise position, so it is also called the tortoise peak. A solid rear blocks wind and gives something to lean on, which is why the form school checks it first. It is exactly what MYEONG looks for as the 'mountain behind' in its siting test.
Related landforms
Source: Standard form-school feng shui (Xingqi) — the landform tradition