What is the term for a very steep slope of rock or clay?

The term that describes a very steep slope of rock or clay is "cliff." A cliff typically refers to a vertical or near-vertical rock face, which can rise dramatically above the surrounding landscape. Cliffs are commonly found in locations such as coastlines, mountains, and along riverbanks, where erosion has created steep rock formations.

In geological terms, a cliff indicates a significant drop in elevation and represents a dramatic change in terrain. The formation of cliffs is influenced by various natural processes, including erosion, weathering, and geological activity, making them distinctive landforms in many environments.

On the other hand, the other terms mentioned represent different features of terrain. A hill describes a raised area of land that is not as steep or tall as a mountain. An incline refers to any slope or upward grade, which may not necessarily be steep. Gradient refers to the degree of steepness or the rate of change in elevation, but it is more of a descriptive term rather than a specific type of landform. Hence, "cliff" is the precise term that accurately depicts a steep slope made up of rock or clay.