成唯識論述記 8.590

8.590

述曰：此釋名也。以此異熟身命短長，或一歲、一日乃至八萬劫等，隨往業因、惑緣之力，有爾所時，若身、若命，定齊限故，名為分段，可為一分一段等，故名分段也。

The Commentary states: This explains the name. Because this retributive body and lifespan may be short or long—either one year, one day, up to eighty thousand kalpas, etc.—in accordance with the power of past karmic causes and affliction conditions, lasting for such a duration, whether body or lifespan, having fixed and determined limits, it is called demarcated segments; because it can form one segment, one division, etc., it is called demarcated segments.