means The layer of Earth's atmosphere above the mesosphere, roughly 80 to 600 km up, where the thin gas absorbs solar radiation and soars to extreme temperatures.

from Built from Greek 'thermos' (hot) — the same root behind 'thermometer' and the vacuum 'thermos' flask — plus 'sphaira' (ball, globe), source of 'sphere.' A modern scientific coinage following the pattern of 'atmosphere' and 'stratosphere,' it names the hottest layer for what it does: drink in the Sun's energy and burn.