Each world has at its centre a Mount Meru surrounded by seven oceans and seven rings of golden mountains separating them. Outside are the four continents and eight subcontinents (two out at sea, left and right of each of the continents). We humans live on the southern continent called “Jambudvipa”. This entire world is then surrounded by the outer iron mountains.
One thousand of such worlds constitute a 'thousandfold world system' (Skt. sāhasracūḍikalokadhātu). A thousand of these makes up a 'second-order thousandfold world system' (Skt. dvitīyamadhyama sāhasralokadhātu). Then, when multiplied a thousand times further, this makes a 'third-order world system' or 'trichiliocosm', a universe of a billion worlds (Skt. trisāhasra mahāssāhasralokadhātu; Tib. སྟོང་གསུམ་གྱི་འཇིག་རྟེན་ཁམས་, Wyl. stong gsum gyi 'jig rten khams). It is said that a single supreme nirmanakaya buddha has mastery over such a world system.
- a billion-fold universe
- a third-order thousand world system
- a third-order great universal system of one thousand million worlds
- a cosmos of a billion universes
- a billion-fold world-system
- Jamgön Kongtrul, Myriad Worlds (Ithaca: Snow Lion, 1995), pages 102-3, ISBN 978-1559391887