means The layer of Earth's upper atmosphere, roughly 50 to 600 miles up, where solar radiation knocks electrons off atoms to create charged particles that can reflect radio waves.

from A 20th-century coinage from 'ion' plus 'sphere.' 'Ion' comes from the Greek 'ion,' meaning 'going' (the present participle of 'ienai,' to go), chosen by Michael Faraday's circle because these charged particles travel toward electrodes. 'Sphere' traces back to Greek 'sphaira,' a ball or globe. So the name literally means 'the going-particle ball' wrapped around the planet — the region defined by its restless, traveling charges.