(1) Duff is a general term referring to the organic layer on top of mineral soil. This layer consists of fallen vegetative matter in the process of decomposition. It includes everything from litter on the surface to pure humus. It is also known as: "humus", "leaf litter", "organic matter", and "forest litter".
(2) Duff is also defined as a layer of decaying organic plant matter (leaves, needles, and humus) on the ground. It is highly absorbent, but quickly erodes under foot traffic.
(3) A matted layer of decaying organic plant matter (leaves, needles, and so on) characteristic of forested soils.
(4) Duff: Any combination of loose vegetation, vegetable matter, roots, and organic-laden soil. Duff retains moisture and rots quickly if not removed from trails, resulting in the formation of depressions and pockets that retain water and tend to erode.
(5) Forest litter and other organic debris in various stages of decomposition on top of mineral soil.
Duff is typical of coniferous forests in cool climates where the decomposition is slow and litter accumulates.
(1) A thick layer of duff in the forest makes for quiet, soft walking.
(2) I like walking on duff because it's soft.
(3) Humus us a jaunty tune, Duke, while we dance on the duff.