Definitions for "Epistles"
Letters written under inspiration of the Holy Spirit, to be read as instruction to the churches. "I charge you by the Lord that this epistle be read to all the holy brethren" (1 Thes. 5:27).
Letters to Christian communities, such as Paul's Epistles.
The word "epistle" is from the Greek word epistolos which means a written "letter" addressed to a recipient or recipients, perhaps part of exchanged correspondence. Today in common usage this somewhat elevated term usually connotes a specific group of books in the New Testament that either were letters or were written in that literary form, although "epistle" can refer to other written missives as well, such as a bishop's open letter to the congregants of his see. Calling a letter an "epistle" does not by itself imply that the letter is part of the New Testament, inspired, or even that it is necessarily religious in nature.