ABSTRACT
There are three states of matter: solid, liquid and gas in general to a common people. Through exchange of energy, any one of the states can be converted to other state. For example, H2O molecule is a simple example, as it is available and seen in all these three states: ice (solid), water (liquid) and steam (gas). If energy is supplied to a matter which is in gaseous state, it breaks the molecules into its component atoms and these atoms are stripped off their negative (electrons) and positive (ions) charged particles. This state of matter for which charged particles as well as neutral particles survive at the same time is normally known as plasma.
This chapter discusses about an overview on the existence of plasmas in nature, such as, planetarynebulae, hot stars, interstellar medium and upper atmosphere of the earth. This chapter also present basic concepts of plasmas, such as, concept of temperature in plasma, existence of several temperatures in plasma, quasineutrality in plasma,Debye length and Debye sphere, criteria for plasma, plasma frequency, fluid description of plasmas and corresponding basic equations.
