Which term describes a rapid rock or earth movement that can involve free fall?

The term that best describes a rapid rock or earth movement involving free fall is "fall." This type of movement generally refers to a scenario where material, such as rock or soil, detaches from a steep slope or cliff and descends vertically due to gravity.

This process can occur in various terrain configurations, such as cliffs or steep hill slopes, and usually involves a sudden and often catastrophic release of material. The key characteristic of a "fall" is that the material moves in a free-fall manner as it separates from the slope, leading to potential impacts at the base of the slope.

In contrast, the other terms represent different types of movement: a "slide" generally refers to material moving along a surface, typically at a slower pace and not involving free fall; "flow" describes a more fluid-like movement of saturated materials, often associated with mudflows; and "slip" is commonly used to denote sliding movements along a plane but does not imply the free-fall aspect associated with the term "fall."