Uncluttered - Imagine a bedroom, your bedroom. You didn't clean it for weeks! There's papers, dust, clothes, all over the floor! You can barely see the floor anymore. - Now you decide to clean it up. And suddenly, you can see the floor again. Now go back to the word 'uncluttered'. I just explained the word by using your dirty room as an example. So, uncluttered; no elements or objects are blocking the view of that what is actually important; the floor in your room. If it is filled with stuff you can't see it anymore, and becomes 'cluttered' and 'unclear'. An 'uncluttered' website in this case, means it's easy to navigate. (the main elements are clearly shown) And it's therefore 'clear' and 'clean'.