Plasma is the fourth state of matter. To my understanding it's a viscous liquid (semisolid) that is held at a temperature high above what would make most things vaporize.
In physics and chemistry, plasma is a substance similar to gas in which a certain portion of the particles are ionized. The presence of a non-negligible number of charge carriers makes the plasma electrically conductive so that it responds strongly to electromagnetic fields. Plasma, therefore, has properties quite unlike those of solids, liquids, or gases and is considered to be a distinct state of matter. Like gas, plasma does not have a definite shape or a definite volume unless enclosed in a container; unlike gas, in the influence of a magnetic field, it may form structures such as filaments, beams and double layers. Some common plasmas are stars and neon signs.
I don't mind Prime's reinvention of the Plasma Beam as much as its reinvention of the Wave Beam. Electricity isn't a wave, goddammit.
Whatever our other complaints about Other M, I think we can all agree it brought the classic beams from Super into 3D beautifully. I just wish the Spazer were along for the ride. And I was especially impressed with the new mechanics of the Wave Beam. I was annoyed at first when Prime's Wave didn't go through walls, but then I realized it wouldn't work in 3D since you can't see what's on the other side. Other M's transparent walls are an ingenious compromise.