What is plasma?

it's the fourth state of matter.

As you know by increasing temperature or losing pressure matter can transform from solid to liquid to gas and then to plasma so plasma can be produced be adding energy to a gas till all electrons leave its atom and becomes only a nucleus and that's what we call complete ionization. (if these conditions are ended, the atom will transmit the energy which ionized it and return to the gaseous or its natural state). so the atom now is separated electrons and nucleus (negative and positive charges) so it reacts strongly with magnetic fields which you can hold it by, and can conduct electricity stronger than copper and maybe even stronger than the super conductors. you can find the plasma state in nature in stars like the sun and artificially in fluorescence lambs.