What was phlogiston?

The phlogiston theory was an obsolete scientific theory that postulated that a fire-like element called phlogiston is contained within combustible bodies and released during combustion. The name comes from the Ancient Greek phlogistón (burning up), from phlóx (flame). It was first stated in 1667 by Johann Joachim Becher. The theory attempted to explain burning processes such as combustion and rusting, which are now collectively known as oxidation.