The part of the Earth's atmosphere beginning at an altitude of about 50 kilometers (31 miles) and extending outward 500 kilometers (310 miles) or more.

(archaic) In a complex manner.

Initialism of Synchronous Code Division Multiple Access.

(geothermal energy) Initialism of Hot Dry Rock. / Initialism of Humanitarian Daily Ration. / (photography) Initialism of High Dynamic Range.