Plasma is a gas containing electrically charged particles. Suitable propulsion systems produce plasma and use electric and magnetic fields to control particles and accelerate material outward. The spacecraft receives thrust in the opposite direction. Propellant and an energy source are still required.
Hall thrusters are an established example of electric plasma propulsion. A magnetic field influences electron motion, while an electric field accelerates ions. Other designs arrange the process differently. “Plasma engine” is therefore not a sufficient technical specification, and ion propulsion overlaps with plasma propulsion rather than forming an entirely separate family.
For suitable missions, efficient propellant use can accumulate a large velocity change over time. Available electrical power and relatively low thrust constrain applications. These systems serve orbital maneuvers and spaceflight rather than simply replacing launch rockets. A glowing exhaust does not imply nuclear fusion or exotic physics. Assessing a new claim requires measured thrust, power and a stated acceleration mechanism.