Degassed water is like water that has had all the little bubbles taken out of it. Imagine if you blow bubbles into your juice, it becomes a bit bubbly and fizzy. That's because there's air trapped inside the bubbles. Well, degassed water is just water that's had all those little bubbles taken out, so it's not fizzy anymore.
This happens because when water is exposed to air, it can absorb some of the air's gases, like oxygen and carbon dioxide. These gases can cause bubbles to form, which makes the water fizzy or bubbly. But if you take the water and put it in a special machine that removes those gases, you're left with degassed water.
This type of water can be used in a lot of scientific experiments and industrial processes where having no bubbles is really important. It can also be used in things like medical and pharmaceutical applications where a really pure form of water is needed.
So in summary, degassed water is water that's had all the little bubbles taken out of it, and it's really useful in many different ways!