ELI5: Explain Like I'm 5

Indefinite monism

Indefinite monism is the belief that everything in the universe is made of one substance, but that this substance is not a particular kind of thing. This means that it is not made of atoms, or energy, or matter, but instead is made of something that is everywhere, everywhere around us and in everything. That means that you, me, and everything else in the world is actually all made out of the same stuff!