The forms or phases in which matter may occur, based on the kinetic energy of its atoms or molecules. Classically, matter may exist as a gas (e.g. water vapour), liquid (e.g. water), or solid (e.g. ice). A plasma constitutes a fourth state, in which a gas loses or gains electrons (is ionized), giving it a positive or negative charge, leading to the dissolution of molecular bonds and the acquisition of properties different from those of the other three states. At extremely high temperatures it is thought that free quarks and gluons may exist in a state called a quark-gluon plasma. At a temperature close to 0 K, in a very tenuous gas composed of bosons, many of the bosons occupy their lowest quantum state and exhibit properties including superfluidity and superconductivity; the bosons are then said to be in a distinct state called a Bose–Einstein condensate. At still lower temperatures fermions form a similar condensate, known as a fermionic condensate, at which superfluidity occurs.