When things get really hot, they sometimes start to move around and bump into each other a lot. This happens to some chemicals too. When chemicals are in a liquid and they are heated up, they start moving around a lot and bumping into each other.
The problem is, sometimes this movement makes it hard for the chemicals to get from one place to another. It's like if you were in a big crowd of people and trying to get through them. You might get stuck or slowed down because there are so many other people around.
The Debye-Falkenhagen effect is a way to measure how fast chemicals can move through a liquid when it's heated up. Scientists use special tools to measure how quickly chemicals can move through a liquid as it's heated up. They named it after two scientists who figured out how to do this kind of measurement.
By measuring the Debye-Falkenhagen effect, scientists can learn how different chemicals move through different kinds of liquids when they are heated up. This helps them understand how chemicals behave in different situations, which can be really useful for all sorts of things!