It is a type of karma which is responsible for the life-span of the soul in a particular realm.
It has four sub-types:
1
Devāyusya
life-span-determining in the realm of gods
2
Manusyāyusya
life-span-determining in the realm of humans
3
Tiryañcāyusya
life-span-determining in the realm of sub-humans
4
Nārakāyusya
life-span-determining in the realm of infernals
The first two sub-types are auspicious, the last two are inauspicious. Only a soul in the second sub-type (i.e., human-life-span) can attain emancipation. Unless the āyusya karma is completely annihilated, the soul cannot attain emancipation.
Life-span-determining karma