chord tones; basically the notes in the chords you are playin over (eg root 3rd 5 7th or whatever. these notes anchor the lead to the rythm so they sound connected. too many and it sounds boaring to few and it sounds too random. try and settle on these tones and play them for longer or play one when the chord changes. this will help make the music fit/
scale tones; notes in the scale or scales you can use over several chords which contain notes that 'fit' with those played by the chord but are not in the chord. so like if i am playing Cmaj7 which would suggest ionion, the scale tones would be te second fourth and sixth.
passing tones; these are tones not in the key, they are often refered to as chromatics. an important part of them as they go from a note not in the key to one of the chord tones, or fill the gap between a scale tone and a chord tone, or a chord tone and a scale tone. they kind of fill the gaps. these can be used to make the music sound very silky and flowing and in some cases like the blues can be used to resolve from an incorect tone to the correct one, eg the minor third being bent the the majour one.
extensions; these notes are notes not in the chord that can build on the chord to make it more interesting like adding a flat or natural 2 to the minor chord being p[layed by the rythm. the thing about extensions is they dont have to be scale tones but can be. you then might say well arnt extensions just passing tones or scale tones, well no. extensions have to be phrassed in a certain way. they should normall follow a chord tone and should move by an interval larger than a third. also try to hold them for longer time so they have longer harmonic relevance.
scale tones extensions and passing tones add richness and the chord tones anchor the music. together if used properly and intelligently very creative and diverse music can be produced.
anyway hope this helps it really made this whole subject make a lot more sense to me. in the end remember theory is a guide not a rule, but although it ccan be good to stray from the path there is also much to be learnt from it.
