'I'm going to ghost the third note'... that's the best jazz language comment I've heard for years
The curious thing about ghosting notes is somewhat comparable to painting with water colours: staring at what you're doing and where you're doing it prevents you from seeing the entire body of the painting rather than the detail you're adding. If you do what you're doing manually but keep your eyes on the total/overall composition rather than the square inch you're working on, then the blending of the colours and how thick/dense the strokes are will make your entire finished piece far more harmonic than taking the strict graphic approach.
Ghosting notes on the off-beats is quite a similiar feat: you first study the signature of the rhythm. Is it a 4/4 loop or is it twice that (8/8)? Well, 8/8 beaks down to a four-four anyway, so let's look at the underlying quantization: is it sixteenth notes or thirty-second notes? Which are the most relevant to the groove required? If it's carried as eight notes with the right hand keeping time, then what's your left hand doing in response to that? The right hand's playing hard eight notes so the left can complement that by playing the other eight notes in the overall sixteenth note phrasing.
But if instead of dividing the four whole beats of the bar with your right hand (or eight notes, depending) then the left can fill in the 'missing' or 'ghost' notes and use them to flatter the points in between the full notes to give it more expression.
The triplet variation is rather more complex at first: you count all four beats of the bar: 1, 2, 3, 4 - but instead of using eight notes you divide the space in between each on beat
with three notes instead of two, or four, or even eight. The difference now is that your 4/4 has twelve notes across the entire bar. Each beat having three notes to it. So instead of 1, 2, 3, 4, you now have 1,l,l, 2,l,l, 3,l,l, 4,l,l. The hard notes are played on the fourths and the spaces in between can be ghosted with the other two triplet notes your left hand is playing against the right hand.
ONE and
TWO and
THREE and
FOUR and
As opposed to:
ONE, la,la,
TWO, la,la,
THREE, la,la,
FOUR, la,la.
They're both played at the same tempo, but the first lopes along like any 'white man's' beat you know and like: it's four beats long, is carried by eight notes, can be sub-divided into sixteenth notes, thirty-second notes, or even sixty-fourth notes, if you're adept enough to carrying it. The second, on the other hand (literally) opens up the possibilities of using triplet note figures divided down into twelfths, or twenty-fourths, or forty-eights. It's the difference between swing and steady. Jazz players specialize in sub-division of notes, whether on the piano, sax, or even drums. A track like 'Take Five' has five beats to the bar, but Joe Morello uses the fifth-note bar and sub-divides each beat first into triplets, and then into twelfths, and even deeper into twenty-fourths, while still carrying a 5/4 groove.
When an odd time signature (5, 7, 9, 11, 13) loop is being used, the other instruments can then sub-divide their parts as fours (for example) meaning it'll take five bars of real time for them to resolve their loop against yours. Same rules apply to straight time signatures (2, 4, 8, 16, 32). But then you also have your natural triplets (3, 6, 12, 24) which are set as triplet form but again can be subdivided and the ghost notes used to best effect in between the hard notes.
Actually, I think Dave Allen explains this (maybe) a bit better than I can: