Extracted from the website of Buddhist Vajrayana Charity Funds Association and translated (娑婆世界) into English:
The Saha World
Buddhism has its theory on how the earth was formed: it was initially regarded as a mass of foam and gradually condensed into solid. According to Buddhism, the earth also belongs to the 'World of Mechanics'. Therefore, its development must go through the principle of the four stages: formation, existence, deterioration and emptiness.
One ‘Three Thousand Great Thousand World’ is one Buddha Land. It is the real world where Buddha Sakyamuni educates sentient beings, including human beings, and is also known as the “Saha World”. Saha is the Sanskrit phonetic translation, translated as mixed evil and mixed societies. The meaning is tolerance, endurance, be able to bear, and soil of endurance. Thus, sentient beings of this realm being accustomed to the ten evils, endure various worries and refuse to renounce; hence known as tolerance. This is why the Saha World is the world where sentient beings of the six realms mix together miscellaneously. In addition, Bodhisattvas who commit to the Bodhi path, also go through the virtue of endurance of all worries, representing fearlessness and benevolence. Therefore, the Saha World is also known as the ‘Soil of Endurance’ or the ‘World of Endurance’.
Moreover, the term Saha originally refers to the Jambudvipa(continent of the terrestrial world)where I and sentient beings live. This later became the Three Thousand Great Thousand Worlds where Buddha Sakyamuni preached. Saha is therefore summarily called the World of Billion Mountain Meru or Sumeru(sacred mountain in Buddhist tradition). The Buddha is therefore regarded as the Fundamental Master of the Saha World.
Remarks
Here are a few simple and basic concepts:
Buddhism explains the structure of a world(小世界). Each world has a Sun, a Moon and Mountain Meru (須彌山). This world is not exactly a solar system.
•	One ‘Small Thousand World’(小千世界) is formed by one thousand worlds. [one ‘Small Thousand World’ = world x 1000]
•	One ‘Medium Thousand World’(中千世界) is formed by one thousand ‘Small Thousand Worlds’. [one ‘Medium Thousand World’ = Small Thousand World x 1000]
•	One ‘Great Thousand World’(大千世界) is formed by one thousand ‘Medium Thousand Worlds’. [one ‘Great Thousand World’ = Medium Thousand World x 1000]
‘Great Thousand World(大千世界)’ is also known as ‘Three Thousand Great Thousand World(三千大千世界)’ or ‘Three Thousand World(三千世界)’. It does not mean that there are three thousand ‘Great Thousand World’. It is just a name of the world. It refers to one ‘Great Thousand World’ which embodies ‘Great Thousand’, ‘Medium Thousand’ and ‘Small Thousand’. That is, ‘Great Thousand World’= ‘Three Thousand Great Thousand World’= one Buddha Land