The kerusso terms [kerysso, keryx, kerygma] represent a more dramatic form of communication, that of a herald, a proclamation.
Preaching (kerussein) in the NT tends to be used most of for the proclamation of the gospel to a group for the first time, so it is associated with the most basic elements of the gospel. Jesus engaged in preaching, but the NT uses the term most often to refer to the apostolic proclamation, especially that of Paul. The apostles preached Christ to Jews in their synagogues (as Acts 9:20), to Samaritans (8:5), and to Gentiles in their cities (14:1-7).
We are accustomed to think of preaching as what takes place in our Sunday-morning sermons. But it is perhaps significant that the NT never uses kerusso terminology to refer to anything in the Christian worship service.
The Doctrine of the Word of God | p 259 | John Frame -- In this section Dr. Frame is comparing preaching to teaching, kerysso to didasko. I mostly pulled, obviously, from the kerysso parts. For context, Dr. Frame says, "The didasko terms seem especially appropriate in a church context" because it broadly refers "to communication of ideas." He sees some overlap, but I felt the "preaching" part was particularly helpful in the open-air/public preaching discussion.