Inauspicious year. A relic of complex onmyo-do calculations which took into account place, time and year of the subject's birth as well as the changing directions of dangerous deities such as konjin. Yakudoshi are normally considered nowadays to be the age of 33 for a woman and 42 for a man. At these ages people often like to be involved in Shinto or Buddhist ceremonies and at least purchase special protective amulets (o-mamori) in order to offset their bad luck.
A Popular Dictionary of Shinto. Brian Bocking.