You had apps like Konqueror (web browser, file manager), KMail (email client), Kompose (music score editor), KImages (later rebranded to Krita), and KDevelop (software dev IDE).
Modern KDE apps dropped the 'K' prefix and moved to a more recognizable scheme, like: Falkon (web browser), Dolphin (file manager), and Okular (document viewer).
As you can see, its now a mix of whether the app keeps the 'K' in the name. Some do not.