Question: How are the Sahā World and Saṃsāra different and similar?
Answer: The Sahā World (娑婆世界) which means the ‘World Of Endurance’ [of suffering] (堪忍世界) refers to our world system, in terms of our galaxy, the Milky Way (银河).
Saṃsāra (生死轮回) means the ‘cycle of (re)births and (re)deaths’. Thus, the Sahā World is a part of Saṃsāra, as there are other galactic systems in the universe with beings trapped in rebirth too, thus also being ‘saṃsāric’.
The Sahā World has a complete set of the six realms (六道), of hell-beings, hungry ghosts, animals, humans, asuras and gods. This might not be so for other world systems with different collective karmic expressions, which lead to some realms, such as that of hell-beings possibly being (empty or) missing, even if for a limited period of time, until karmic conditions change.