From Slashdot: http://www.eetimes.com/showArticle.jhtml?articleID=209800332
In physics, a plasmon is a quantum of a plasma oscillation. The plasmon is the quasiparticle resulting from the quantization of plasma oscillations just as photons and phonons are quantizations of light and sound waves, respectively. Thus, plasmons are collective oscillations of the free electron gas density, often at optical frequencies. They can also couple with a photon to create a third quasiparticle called a plasma polariton.