This word episkopos (from which we get Episcopal) is used a total of 5 times in the New Testament, always in reference to someone who has authority to lead in ministry. It is usually translated "overseer" or "bishop." Clearly, it is a position of leadership, most commonly thought to refer to the position of pastor. The difficulty in understanding the full meaning of this word comes when we try to compare it to the second word used in scripture for leadership: presbuteros.
Presbuteros
The word presbuteros occurs 72 times in the New Testament, and it has a range of meanings. The majority of the time (57 times) it is translated "elder" and means a position of leadership in the church, like a pastor or other member of church leadership.
Diakonos
The word diakonos means “one who serves in ministry” or more generally, "servant." The word appears 29 times in the New Testament. Of those 29 times, it is translated (by the NASB) as "deacon" three times, as "minister" seven times, and as "servant" 19 times. Consequently, the best definition of the duties of a diakonos is one who ministers to the church through their service.
with thanks to: http://www.versebyverseministry.org/articles/detail/presbuteros_episkopos_diakonos/