Ziyarat means visitation. In the Islamic sense, this term is primarily used for the visitation of the graves of the vice-regents[1] of Allah (Khulafaa Allah) who include Allah’s messengers, prophets, and their executors. Ziyarat literature is a formal liturgical expression used by the faithful while visiting the shrines of Prophet Muhammad (PBUH&HF) and his Ahl al-Bait (PBUT),[2] and can also be recited to address them from afar. Much of the Ziyarat literature was recited and transmitted by the infallible Imams (PBUT) and was recorded in the books of traditions.
[1] The vice-regents of Allah on earth are His deputies and representatives who are chosen and authorized by Him over the creation while Allah preserves His authority and sovereignty. He has defined submission to His representatives as submission to Him since they act according to His command. C.f. the holy Quran, 4:59, 4:64-65, 4:80, 8:20, 21:26-28, 21:73, and 48:10.
[2] Ahl al-Bait means People of the House. However, the Ahl al-Bait of the Prophet (PBUH&HF) as specifically defined by him and believed by the Shia, refers only to the divinely selected individuals of his house. They are his daughter (Lady Fatima (PBUH)) as well as twelve divinely appointed leaders (Imams) who were the executors and spiritual successors of the Prophet (PBUH&HF). The twelve Imams include the Prophet’s son in law and cousin, Ali (PBUH), Ali’s two sons, al-Hasan and al-Husain (PBUT), as well as nine descendants of al-Husain (PBUH). The acronym “PBUT” refers to phrase “peace be upon them.” In addition, “PBUH&HF” refers to phrase “peace be upon him and his family.”