Rick,

From an experiment about 150 years ago, scientist Fizeau did get a lot of data about the time it took for a beam of light to get from a to b.

This is data

From the data he could calculate that the speed of light in his experiment was approx 300.000 km/s

This is information

From the information of other experiments and existing theories done by other scientists, we learned that the the speed of light in vacuum is a constant.

This is knowledge.

But

We still do not understand the underlying physics on the quantum level.