Asking the distributed mind

I'm trying to figure out what needs to be in one of the high school review/test prep books we're doing. Mostly it's going okay--sometimes frustrating, but I know what they want and can therefore figure out how to cover it. This is an exception.

The Illinois high school science standard says "Understand the reflection, refraction, diffraction, interference, and frame of reference properties of waves." All clear except for the last phrase.

My best guess is that they want students to know that the speed of light doesn't change depending on your frame of reference. Can anyone confirm that or show me that I'm on the wrong track here.

Googling isn't much help, it mostly gets me either odd question/discussion forums or sites connected to Illinois school, just quoting the wording of the standard.