Jingu is the formal name of Ise-jingu Shrine (Ise City, Mie Prefecture). There are also many other shrines with the title jingu in their names.
In Nihon Shoki, only Ise-jingu Shrine and Isonokami-jingu Shrine are recorded as having the title 'jingu.'
Following this, Kashima-jingu Shrine and Katori-jingu Shrine were listed in place of Isonokami-jingu Shrine in the Jimmyocho (register of deities) of Engishiki law during the Heian period and, until the Edo period, there were only three shrines with the title 'jingu' (Sumiyoshi Taisha Shrine was also treated as a jingu as it was under direct royal control like Ise-jingu Shrine and regularly conducted the construction of a new shrine and the transfer of the enshrined object from the old to the new).
After the end of the Meiji period, some shrines enshrining the ancestral gods of the imperial household, emperors or specific gods that conducted great deeds during the conquer of Yamato changed their titles from 'jinja' to 'jingu.'
Until the end of the Second World War, a shrine required imperial permission in order to use the title 'jingu.'
The national administration of shrines was abolished after the war but even now shrines with the title 'jingu' are limited only to those with especially distinguished histories. Only 3 shrines changed their titles to 'jingu' after the war and all of these did so with the special permission of Association of Shinto Shrines (Hokkaido-jingu Shrine (formerly Sapporo-jinja Shrine), Izanagi-jingu Shrine (Hyogo Prefecture), Hikosan-jingu Shrine (Fukuoka Prefecture).
The deity Amaterasu Omikami enshrined within Ise-jingu Shrine (Kotai-jingu Shrine) has been divided and shared with numerous shrines around the country carrying the titles of 'Daijingu' and 'Kotaijingu,' but these titles are accepted as being different from that of 'Jingu.'
Please also refer to the name 'Jinja.'
A list of Jingu Shrines
Three Main Jingu Shrines
The three most representative jingu shrines of those listed above are referred to as the san dai jingu or san jingu. As one of Shrine Shinto's most important sites, Ise-jingu Shrine is always included, whereas the other two are differently considered to be the following combinations.
The first of these is Ise-jingu Shrine, Kashima-jingu Shrine and Katori-jingu Shrine as the three shrines to have held the title of 'jingu' since before the Edo period.
The second is Ise-Jingu Shrine and Atsuta Jingu-shrine, chosen for their deep relationship with the imperial household and possession of the three sacred treasures in which deities reside, and the third is Heian-jingu Shrine or Meiji-jingu Shrine despite the lack of history.
The name Jingu always refers to Ise-jingu shrine and can not be used to compare other shrines to Ise-jingu shrine.