The measure of the change in elevation over a certain distance is called gradient or slope.

Here's a breakdown:

* Gradient: This term is often used in mathematics and is expressed as a ratio, typically "rise over run."

* Rise: The vertical change in elevation.

* Run: The horizontal distance.

* Slope: This term is commonly used in geography and engineering. It can be expressed as a percentage, a ratio, or an angle.

For example:

Imagine a road that rises 100 meters over a distance of 1 kilometer (1000 meters).

* Gradient: 100 meters / 1000 meters = 1/10

* Slope (as a percentage): (100 meters / 1000 meters) * 100% = 10%

Important Note: Gradient and slope are essentially the same concept, just expressed in different ways.