KDE: Disable touchpad while typing
Solution 1:
Application menu -> Utilities -> touchpad management. There, you can ask the system to disable the touchpad when a usb mouse is connected and/or when you are typing.
Solution 2:
KDE 4 or 5
KDE 4: sudo apt install kde-touchpad
kcmshell5 kcm_touchpad or kcmshell4 kcm_touchpad
And you'll even have an option to disable touch and scroll only, leaving you the ability to move the cursor.