Plasma is defined in Websters as a ”collection of charged particles ... containing about equal numbers of positive ions and electrons and exhibiting some properties of a gas but differing from a gas in being a good conductor of electricity ...”. You can also think of it as an electrically heated gas stream. I like to think of it as a condition where all of the electrons from every atom are flowing from atom-to-atom, instead of just orbiting. Regardless of what’s going on inside a plasma stream, the way to cut metals with it is pretty straightforward. Take that stream of electricity flowing through a gas, and constrict it through a small orifice. Now that stream is really dense and moving very fast. The resulting stream can melt and blow through most metals quite easily. That’s a plasma torch.