quasiparticles

Quasiparticles are phenomena in physics that behave like particles but aren't fundamental particles themselves.

They emerge from collective behavior in complex systems—an electron moving through a crystal lattice, for instance, interacts with surrounding atoms in ways that make it act as if it had different mass or charge.

Phonons (quantized vibrations), polarons, and Cooper pairs are quasiparticles.

The concept lets physicists treat complicated many-body problems as if they involved simpler, independent entities.