Technically refers to a form of matter made of neutrons compressed together by gravity, but is most commonly a colloquial term for a form of metal, usually aluminum, which has been manufactured under specific, highly controlled circumstances that vastly reduces the space between atoms, making it stronger, more rigid, heavier and stable in its compressed state. May also be used to refer to non-metals made to the same standards. It’s often an (ironically, given the name) lighter-weight or cheaper substitute for charybdinium.