What does "Open Source" mean in this context? Isn't the goal "just" to have an understandable interface?

Also: Can you recommend some reading material as an introduction to using a capacitive digitizer? I am planning to use one in an upcoming project (either one from a tablet glass replacement or a stand alone one) and really have no idea what to look out for yet in terms of communication with my Linux board (bonus: Something about DIYing one because I need a special format, but I guess that's especially hard because it's supposed to go on to a screen).