A bishop is an English translation of the Koine Greek word episkopos found in various places in the New Testament. The word can also be translated "guardian" or "overseer".
In Christianity, a bishop is an ordained clergy person who is given authority over the Church and responsibility and guardianship over the Christian Faith. Bishops also serve as administrative leaders in denominations with [episcopal](Episcopal(polity))_ forms of church polity.
- Acts 20:28 - refers to the episcopal role equated in some way with that of the Elder (presbuteros)
"Pay careful attention to yourselves and to all the flock, in which the Holy Spirit has made you overseers [episkopoi...in this verse, the traditional translation of episkopos has been overseers], to care for the church of God, which he obtained with his own blood." - Philippians 1:1 - simply mentions the existence of bishops
"Paul and Timothy, servants of Jesus Christ, to all the saints in Christ Jesus which are at Philippi, with the bishops and deacons..." - 1 Timothy 3:1-7 - some qualifications for the episcopacy
"This saying is true: whoever aspires to the office of bishop desires a noble task. Now a bishop must be above reproach, married only once, temperate, sensible, respectable, hospitable, an apt teacher, not a drunkard, not violent but gentle, not quarrelsome, and not a lover of money. He must manage his own household well, keeping his children submissive and respectful in every way - for if someone does not know how to manage his own household, how can he take care of God's church? He must not be a recent convert, or he may be puffed up with conceit and fall into the condemnation of the devil. Moreover, he must be well thought of by outsiders, so that he may not fall into disgrace and the snare of the devil." - Titus 1:7-9 - some qualifications for the episcopacy
"...a bishop, as God's steward, must be blameless, not arrogant or quick-tempered or addicted to wine or violent or greedy for gain, but hospitable, a lover of goodness, prudent, upright, devout, and self-controlled. He must have a firm grasp of the word that is trustworthy in accordance with the teaching, so that he may be able both to preach with sound doctrine and to refute those who contradict it." - 1 Peter 2:25 - reference to Christ as the Bishop par excellence
"For you were straying like sheep, but have now returned to the Shepherd and Bishop of your souls."
Early Church & Eastern Orthodoxy
"Scholars are virtually unanimous that in the early church the presbuteros and the episkopos were one and the same. Indeed, there is no clear evidence for a monarchical episcopate being firmly established until the early decades of the second century." - Baker's Evangelical Dictionary of Biblical Theology ("Overseer" entry)
By 200 AD, bishops were ordained clergy charged with overseeing large cities or regions, presiding over the churches of their assigned area. At some point, the offices of episkopos (bishop) and presbuteros (elder) were separated, with elders serving a more localized pastoral function and bishops overseeing their work.
In Presbyterian churches, episcopal authority is generally viewed to be vested in the local presbytery. Some traditions place this authority in a governing board of stewards, while others view the episcopal role as identical with that of the presbyter or presiding elder.