This is the Theosophist concept of hell, which is derived from the Sanskrit for "isolation." Although a place of torment it greatly differs from the ordinary conception of hell, chiefly because those who reside there have no physical bodies with which to satisfy the fleshy desires that they are plagued with.
The Theosophical teaching on which Avichi is based is the conception that people remain the same entity after death as they were before dying. That is, if in life a person was possessed by strong passions and desires then he will retain them in the astral world. The desires then become unsatisfying with a physic body and turn into anguished torments.
The manner of torments seems to be infinite varying from the confirmed sensualist struggling with his desire of the flesh to the ordinary person, while not burden be fleshy desires, who is troubled by the thought that he gave too much attention in his earthly life to worldly affairs rather than focusing on higher goals. This latter person is thus doomed to regret his lack of attention toward higher objectives.
Avich is a place of regrets for things done and left undone in the physical life. Its torments, however, are not eternal, but will gradually subside after timeless durations of anguished torment.
Source: 9. 137.