(⌐■_■) (☞゚ヮ゚)☞A priest or priestess, is a religious leader authorized to perform the sacred rituals of a religion, especially as a mediatory agent between humans and one or more deities.
Religion is a cultural system of behaviors and practices, world views, sacred texts, holy places, ethics, and societal organisation that relate humanity to what an anthropologist has called "an order of existence".
A ritual "is a sequence of activities involving gestures, words, and objects, performed in a sequestered place, and performed according to set sequence."
Clergy are some of the main and important formal leaders within certain religions.