The canonical epistles of James, Peter, and Jude, and the first of John, are so called because they are not addressed to any particular individual or church, but to Christians in general (Suicer, Thes. Ecclesiastes 2:15).
Hug gives the following view: "When the Gospels and Acts of the Apostles constituted one peculiar division, the works of Paul also another, there still remained writings of different authors which might likewise form a collection of themselves, to which a name must be given. It might most aptly be called the common collection, καθολικὸν σύνταγμα, of the apostles, and the treatises contained in it κοιναί and καθολικαί, which are commonly used by the Greeks as synonyms. For this we find a proof even in the most ancient ecclesiastical language. Clemens Alexandrinus calls the epistle which was dispatched by the assembly of the apostles (Ac 15:23) the 'catholic epistle,' as that in which all the apostles had a share, τὴν ἐπιστολὴν καθολικὴν τῶν Α᾿ποστόλων ἃπαντων. Hence our seven epistles are catholic, or epistles of all the apostles who are authors" (Introd. to N.T. § 151). So, also, Eichhorn. See Horne, Introduction, pt. 6, ch. 4, § 1. SEE EPISTLES, APOSTOLICAL.