Definitions for "Quasiparticle"
a quantum of energy (in a crystal lattice or other system) that has position and momentum and can in some respects be regarded as a particle
A unit of energy in solid-state physics with mass and momentum but that does not exist as a free particle.
In physics, a quasiparticle refers to a particle-like entity arising in certain systems of interacting particles. It can be thought of as a single particle moving through the system, surrounded by a cloud of other particles that are being pushed out of the way or dragged along by its motion, so that the entire entity moves along somewhat like a free particle. The quasiparticle concept is one of the most important in condensed matter physics, because it is one of the few known ways of simplifying the quantum mechanical many-body problem, and is applicable to an extremely wide range of many-body systems.