Technical Plasma can be stimulated under atmospheric pressure or under low pressure. Atmospheric pressure is stimulated by gas discharge. Because the mean free waypath of ions under atmospheric pressure is very low (10-7 m), the volume of the plasma is concentrated in the area of high voltage.
Low pressure plasma is stimulated by high frequency electric fields, usually between 2 electrodes. Because of the big mean free waypath of ions and radicals under low pressure (10 cm at 10-3 mbar) the volume of the plasma can exceed the limits of the high frequency field and can comprise the complete volume of the recipient.
Basically any gas can be used to stimulate a low pressure plasma. Additionally many substances which are liquid under atmospheric pressure are gases under low pressure conditions and can be used as process gas. The multitude of process gases enables a multitude of plasma processes.