Jellium

Imagine a bunch of tiny little balls all clumped together in a blob. Now, pretend that each of those balls is actually an atom. Jellium is what you get when you smash all those atoms together so tightly that they start to lose their individual identities and become something new altogether.

What you end up with is a kind of gooey substance that's made up of electrons and positively-charged atomic nuclei all mixed together in a giant mess. The electrons are free to move around through the material, but they're still attracted to the positively-charged nuclei.

Scientists call this "jellium" because it's sort of like jello, but made up of atoms and electrons instead of sugar and water. Jellium is a really important concept in physics because it helps us understand how metals conduct electricity and how they interact with light.