This refers to a book of the NT in the form of a letter from an Apostle. All but six of the 27 NT books are of this nature; the exceptions are the four gospels, Acts and Revelation. Paul wrote thirteen: Romans, 1 and 2 Corinthians, Galatians, Ephesians, Philippians, Colossians, 1 and 2 Thessalonians, 1 and 2 Timothy, Titus, and Philemon. Of these Pauline Epistles four (Ephesians, Philippians, Colossians, and Philemon) were written during Paul’s two-year house arrest in Rome and so called the Prison Epistles, with another subgroup are the Pastoral Epistles (1 and 2 Timothy and Titus) written to church leaders and include many teachings regarding practices within the early church. The remaining eight writings are termed General Epistles, as unlike those of Paul, they were not generally written to a specific person or group of people. The author of Hebrews is unknown, James (written by James, the half-brother of Jesus), the apostle Peter wrote 1 and 2 Peter, the apostle John (the same author of the Gospel of John and Revelation) wrote 1 John, 2 John, and 3 John, the Epistle of Jude written by another half-brother of Jesus.