Is plasma unique? The presence of electrons and the importance of charge

During the last century plasmas have been investigated from various perspectives: light production, astrophysics and starlight, thermonuclear fusion and plasma chemistry and processing. Attention has shifted from atomic excitation to molecular conversion and deposition. This paper addresses the essential role of electrons and ions in forming the plasma, of radicals, of charge and of modified surface kinetics. It is made clear that plasma is a non-equilibrium state of matter, which can be best characterized by the electron density. It is concluded that this non-equilibrium transient character of plasma forms its basic nature. The created electrons, radicals and charge lead to a new situation, distinct from high temperature chemistry with different surface conditions. This enables plasmas to be used for new applications with fast time modulation of plasma processes.