A jingu is a Shinto shrine of the highest designation, the title reserved for shrines of particular dignity, most often those closely tied to the imperial house.
The senior grade
Used without qualification the word jingu refers above all to the Grand Shrine of Ise, the shrine of Amaterasu, the sun goddess from whom the imperial line claims descent, and the single most sacred site in Shinto. Other shrines carry the title where they enshrine an emperor or stand in a special relation to the imperial house, such as the shrine of the deified Emperor Meiji in Tokyo. The designation marks rank and dignity rather than a difference in the basic nature of the shrine, which remains the dwelling of a kami.
Rank and its history
The grading of shrines was formalised and politicised in the modern period, when the Meiji state took the shrines under its administration and organised them into a national hierarchy with the imperial shrines at its summit, using the shrine system to bind the nation to the throne. That state framework, State Shinto, was dismantled after 1945, and the shrines became private religious bodies, but the traditional titles of dignity, jingu and taisha, remain in use. The title thus carries both an old sense of a shrine of the first rank and the memory of the period when such ranks were an instrument of the state.