SN 56.46 says:
Mendicants, the boundless desolation of lokantarikā is so utterly dark that even the light of the moon and the sun, so mighty and
powerful, makes no impression.”
Atthi, bhikkhave, lokantarikā aghā asaṃvutā andhakārā andhakāratimisā, yatthamimesaṃ candimasūriyānaṃ evaṃmahiddhikānaṃ evaṃ
mahānubhāvānaṃ ābhāya nānubhontī .
Concise Pali English Dictionary
lokantarika adjective situated between the worlds
The Pali suttas have the stock phrase: "This world & the other world". This seems to have different meanings (such as in MN 26, where the other world appears to refer to lower worlds). But, generally, in the Buddha's society, it meant the ordinary human world and the heavenly world of the Brahmins. Thus, in Buddhism, the 'other world' can be 'heaven' or meditation jhanas; where MN 79 refers to the meditation jhanas as "a world of exclusively pleasant feelings" (ekantasukhassa lokassa).
In other words, lokantarikā in SN 56.46 appears to refer to the 'world' between the world of ordinary worldly sensual life and the world of meditation happiness; what Christians mystics called "the dark night of the soul", which is a period of spiritual desolation suffered by a mystic in which all sense of consolation is removed.
For example, when a person suffers from sever psychological depression, the light of the moon and the sun makes no impression. Similarly, as occurred to Mother Teresa of Calcutta, nothing, not even ideas of Jesus or God, could help her in her spiritual desolation.
Jesus has a very special love for you. [But] as for me--The silence and the emptiness is so great--that I look and do not see,--Listen and
do not hear.
In SN 56.46, the term 'lokantarikā' possibly refers to 'spiritual desolution' or what Christian meditators attempting to overcome the five hindrances called 'the dark night of the soul'.
If you have doubts about my answer, similar to a certain monk in DN 11 Kevatta Sutta, you can ask about the meaning of the term 'lokantarikā' at Sutta Central.