Within a strongly inhomogeous electric field a medium which usually is a gas but also could be a non conductive liquid is ionisized. The Corona is concentrated to an electrode where the electric field is concentrated very much for example to a pin electrode The corona does not yet cause an electric breakdown by a plasma arc but in some cases can be the ignition for this.

Objects in close contact to the Corona can be plasma treated, in particular activated to receive high surface energy for good chemical adhesion,

See ⇒ Corona Treatment

Corona treatment
To create an atmospheric plasma a gas discharge is generated by high voltage and ejected through a nozzle.