Otsu (ōˈtsō) [key], city (1990 pop. 260,018), capital of Shiga prefecture, S Honshu, Japan. It is a tourist center and a port for excursion boats on Lake Biwa. Electrical appliances, textiles, precision instruments, computer components, and machinery are among the city's industrial products. A former imperial seat (2d and 7th cent.), Otsu is the site of Miidera, a 7th-century Buddhist temple, and of the grave of Basho, the famous poet.