The Catacomb Church () is collective name of those representatives of the Russian Orthodox clergy, laity, communities, monasteries, fraternities, etc., who for various reasons, have moved to an illegal position since the 1920s. In a narrow sense, the term "catacomb church" means not just illegal communities, but communities that rejected subordination to the Deputy Patriarchal Locum Tenens Metropolitan Sergius (Stragorodsky) after 1927, and were on anti-soviet positions. The term was popularized in latter sense by the ROCOR during the cold war, first in the Russian Diaspora, and then in the USSR by sending illegal literature there. As a synonym for the "catacomb church" in this sense, the term True Orthodox Church () is also used, but as the historian Mikhail Shkarovsky notes: "the catacombness of the Church do not necessarily mean its intransigence. This term covers all unofficial and therefore not state-controlled church activities"