A bishop (Greek episkopos an overseer) is a high-ranking member of the clergy, present in many Christian churches, including the Roman Catholic, Eastern Orthodox, Anglican, Lutheran (some) and Methodist denominations. A primate or archbishop is usually the highest-ranking bishop in a particular province or nation-state.
He (or she in more liberal denominations) traditionally wears a miter (the pointed headgear designed to look like a tongue of fire reminiscent of those that came upon the Apostles in the upper room following Christ's Ascension) and oversees a regional association of parishes known as a diocese. In most of the churches that are governed by bishops, the bishops are considered to be in apostolic succession. 
A bishop is also a chess piece representing the religious figure described above.