......and DIATONIC exactly means..?

I'm a beginner....
I'm reading lots of books and articles and sometimes i find confusion explaining
what i believe are simple concepts (but of course i'm wrong).
An example is the meaning of DIATONIC.
I've found these meanings.

1) DIATONIC scale means that it goes from Tonic to Tonic
2) DIATONIC scale has it's name from the type of the semitones which are diatonic (two different names)
3) DIATONIC scale is a scale where all the names of the notes are different
4) DIATONIC scales are simply scales with the exact pattern of intervals that we know for the major and the minor.....

any help?

Greets from Italy

This might confuse you more, because it certainly did confuse me, first the easy and most understanding part, and probably the one you are looking for:

In music theory, a diatonic scale (from the Greek διατονικος, meaning "[progressing] through tones", also known as the heptatonia prima and set form 7-35) is a seven note musical scale comprising five whole steps and two half steps, in which the half steps are maximally separated. Thus between each of the two half steps lie either two or three whole steps, with the pattern repeating at the octave:
http://en.wikipedia.org/wiki/Diatonic_scale

And the the part who did confuse me a little bit:
http://en.wikipedia.org/wiki/Diatonic

The Diatonic reference in wikipedia actually has more exceptions that i thought.....lol
I'm reading "Mastering the scales and arpeggios" by James Francis Cooke... and even though i think it's a great book the are some things
that can be really confusing for a newbie...
For example he describes how to form minor scales from major scales...
and in the melodic minor tells to simply play the 3 flatted ascending and the 3,6,7 flatted descending....
I was using another book and the melodic minor are made in a different way....
How can these topics be so confused...?

People often find different ways of writing the same thing so it doesn't feel to them to just be a copy! Others like to write in a complicated way to sound smart, and sometimes people have different views about things and since you are reading their book, you are told their adaptations, wordings and the like, in the end its up to you to pick what works for you. The best teach yourself books are simple and aren't confusing, from selfless people such as Andrew who don't care about pride and more about helping people.

On that note... ANDREW WRITE AND PUBLISH A "Teach yourself piano" book!!! ^___^