What refers to the relative difference in elevation between two or more points?

The term that refers to the relative difference in elevation between two or more points is "relief." Relief is a fundamental concept in geography and landscape architecture, as it helps to describe how varied the terrain is within a given area. It measures the vertical distance between the highest and lowest points in a landscape, providing insights into the topography and physical features of the land.

Understanding relief is crucial for planning and design work, as it affects water drainage, soil erosion, and habitat suitability, among other environmental factors. It also influences human activities like construction, agriculture, and transportation, as steeper areas present different challenges and opportunities compared to flat terrains.

Other terms in the options do not specifically capture this concept of elevation difference. For instance, while "high ground" denotes elevated areas, it does not quantify the difference between points. "Valley depth" refers specifically to the depth of a valley which is a more focused measurement and not a general term for elevation difference. "Elevation gain" usually pertains to climbing or an increase in elevation for a specific path or route rather than indicating the relative difference between distinct points. Thus, "relief" is the most accurate and comprehensive term to describe the relative differences in elevation across a landscape.