So imagine you have a bunch of toys that need to be sorted and organized. You wouldn't want your blocks mixed up with your stuffed animals, right? You might put your blocks in one container and your stuffed animals in another one.
That's kind of what compartmentalization is in engineering. You have different parts of a machine or system, and they need to be separate from each other for safety or efficiency reasons.
For example, if you were building a car, you wouldn't want the gasoline to leak into the passenger compartment where people are sitting. That's why there's a separate gas tank and engine compartment. And if there's a fire in the engine compartment, you don't want it to spread to other parts of the car, so there are firewalls (not the kind you use on a computer!) that help contain the fire in one area.
Compartmentalization might also be used in a laboratory setting. Let's say you're doing an experiment with dangerous chemicals. You wouldn't want those chemicals to accidentally mix with other substances or escape from the lab, so there might be separate rooms or chambers where different parts of the experiment happen.
Overall, compartmentalization means creating separate spaces or barriers between different parts of a system for safety, efficiency, or other reasons.