Here's a breakdown:

* Humus is the dark, rich, crumbly organic matter that forms in soil from the decomposition of plant and animal material over long periods.

* Ancient decayed forests contribute significantly to the formation of humus. The leaves, branches, and other organic matter from these forests decompose over centuries, adding their nutrients and structure to the soil.

* Humus is incredibly beneficial for soil health, improving its water retention, aeration, and nutrient content.

While you might hear terms like "forest soil" or "woodland soil," these aren't specific types of soil. They simply refer to soil found in forested areas. Humus, however, is a specific component of soil that is particularly abundant in areas where ancient forests have decayed over time.