A plasma is a gas of charged particles containing an equal number of free positive and negative charge carriers. It behaves in a quasineutral way when stationary, and looks neutral from outside. A particle is considered free if its potential energy (due to the nearest neighbors) is much smaller than its random kinetic (thermal) energy. So a plasma is hot and ionized. More than 99% of all known matter in the universe is in the plasma state.¹⁾