What is the difference between a letter and an epistle in the New Testament?

In the New Testament, a letter typically refers to a personal or community correspondence, often addressing specific issues or individuals, like the letters of Paul to early Christian communities. An epistle, on the other hand, generally denotes a formal, didactic letter intended for broader audiences, often containing theological teachings or moral guidance. While all epistles are letters, not all letters are classified as epistles; the term "epistle" carries a connotation of authority and significance within the context of Christian scripture.