plasma

Plasma is a state of matter in addition to solid, liquid, and gas. Plasma is gas-like but the atoms are free of molecular bonds and a significant number are ionized. A body of plasma typically includes both positive and negative particles, e.g., ions, electrons, and positrons usually balanced so that the body as a whole is neutral. The threshold distinguishing plasma from gas (i.e., "how much of the material needs to be ionized?") has no universally-used precise definition, but generally reflects the notion that a gas is plasma if it shows distinct qualities of plasma, such as electrical conductivity and interaction with magnetic fields.

The plasma state is maintained by high temperature. Stars such as the Sun are sufficiently hot as to ionize much of their matter, much of the interstellar medium (ISM) is ionized and the intergalactic medium through galaxy clusters is generally highly ionized. Though plasma is rare on Earth, the vast majority of the universe's baryonic matter is plasma.

Plasma is used in technology such as neon signs and plasma displays.

Collisionless plasma is plasma which lack the constant collisions between particles found in a (neutral) gas, i.e., particles passing so close that their directions are decidedly changed. Rather the particles' movements, under the influence of the fields and plasma waves, are not random and such collisions are relatively rare or non-existent. This is common in the low density of the ISM, for example.