System Settings/Web Shortcuts
You may already have noticed that Plasma offers multiple applications to access the web: Konqueror and KRunner (Falkon doesn't have this feature yet). You can add shortcuts so that when typing in KRunner or Konqueror, for example "dd:hello", you open a DuckDuckGo search with the input "hello".
More Information
- KDE official documentation
- Konqueror/Web Shortcuts in UserBase