首楞嚴義疏注經 9.81

9.81

梵云阿那含，此云不還，此天是彼聖所居故，亦名淨居，非同凡夫有漏住故。以定力殊勝，依報亦勝，同在世間，境界各別，舉例可知。

In Sanskrit they are called anāgāmin, which here means 'non-returning'. Because these heavens are the dwelling place of those noble ones, they are also called the Pure Abodes; they are not the residences of ordinary beings with outflows. Through the pre-eminence of their samādhi power, their environmental reward is likewise pre-eminent; though dwelling in the same world, their realms are distinct, as is understood by the analogy given.