The opposite of elementary particle.
As a phisicist once amazingly put it in a talk Ciro watched:
It all depends on how much energy you have to probe nature with. Previously, we thought protons were elementary particles. But then we used more energy and found that they aren't.If some alien race had even less energy, they might not know about electrons at all, and could think that anyons are actually elementary.Being an "elementary particle" is always a possibly temporary label.
Articles by others on the same topic
A quasiparticle is a collective excitation that can be described approximately by particle-like quantum numbers and dynamics, even though it is not an isolated elementary particle. Excitons and polaritons are examples.
