Ksara refers to those who have fallen down
Srimad-Bhagavatam
SB Canto 4
Kṣara refers to those who have fallen down and become conditioned, and akṣara refers to those who are not conditioned.
SB 4.24.28, Purport: By endeavoring to dominate material nature, the living entity simply struggles hard for existence. Indeed, he struggles so hard to enjoy himself that he cannot even enjoy the material resources. Thus he is sometimes called prakṛti, or jīva, for he is situated in the marginal potency. When the living entity is covered with the three modes of material nature, he is called jīva-saṁjñita. There are two kinds of living entities: one is called kṣara, and the other is akṣara. Kṣara refers to those who have fallen down and become conditioned, and akṣara refers to those who are not conditioned. The vast majority of living entities live in the spiritual world and are called akṣara. They are in the position of Brahman, pure spiritual existence. They are different from those who have been conditioned by the three modes of material nature.