The eighth house is the eighth of the twelve houses of the horoscope. It governs death and transformation, inheritance, shared resources and other people's money, and the deep, hidden, and taboo, the sphere of profound change, crisis, and the things held in common with another. It is a succedent house, of moderate strength, following the angular seventh. In classical astrology it was reckoned one of the more difficult and shadowed houses, connected with death. These are the interpretive conventions of the astrological tradition for this division of the chart, in which the eighth house describes what is shared, surrendered, and transformed, the resources joined in partnership and the passages through which a person is remade; it stands opposite the second house of personal possessions across the wheel, the axis of what is one's own against what is shared.
Greek astrologers called the eighth house Argos, the idle or inactive place, and also the place of death, and the Hellenistic scheme that names it this way, already assumed as traditional by Vettius Valens around 175 CE and set out systematically by Paulus Alexandrinus in 378, counted it among the weakest and most difficult of the twelve. No planet was given a joy here, and the tradition's fixation on death is considerably more literal in the ancient sources than in most modern treatments, which tend to soften the eighth into transformation and psychological depth; the older texts are reading a house of actual mortality, danger, and the estate left behind, the shared and inherited resources of a life's ending rather than of a relationship's ongoing finances, which is closer to how the house functions in the earliest surviving practice.
Sources A History of Western AstrologyNicholas Campion with Introduction to Astrology (Eisagogika)Paulus Alexandrinus