The tenth house is the tenth of the twelve houses of the horoscope, and one of the four angular houses, the strongest kind. It begins at the highest point of the chart, the midheaven or medium coeli, and it governs career, vocation, public standing, reputation, and worldly achievement, together with one of the parents and the authority a person attains, the summit of the chart and of a life's outward course. As an angular house it gives planets placed in it much force, and it is often reckoned the most public and elevated of all. These are the interpretive conventions of the astrological tradition for this division of the chart, in which the tenth house describes what a person is known for and rises to; it stands opposite the fourth house of home and roots across the vertical axis of the wheel.
Greek astrologers named the tenth house Mesouranema, the midheaven, describing its geometry directly as the highest point the ecliptic reaches at the moment in question, and the Hellenistic scheme fixing this name, already traditional in Vettius Valens around 175 CE and set out systematically by Paulus Alexandrinus in 378, ranked it among the most powerful of the twelve houses for its visibility alone. No planet was assigned a joy at the midheaven, unlike several of its neighbours, yet its angularity alone made it, alongside the ascendant, the house Hellenistic astrologers watched most closely for questions of public life and reputation. The medieval and later Western tradition's specific emphasis on career and vocation, as opposed to the broader ancient sense of visible standing and action before the world, developed gradually on top of this older angular reading.
Sources A History of Western AstrologyNicholas Campion with Introduction to Astrology (Eisagogika)Paulus Alexandrinus