It means the solid end panels are fixed to the veneer behind with hidden screws in elongated holes to allow for expansion or contraction in the solid end panels.
Sliders= non tech term we tend to use at work............ you can maybe help me Richard with a correct term
Slot screwed is the common term I'd say.
If you look at the images you can see the vertical gaps are filled with an edged veneer set 50mm back. 19mm on the ends and 16mm in the middle 2 gaps, there is then a thin slither placed over the veneer slightly wider to hide the undermounted runners.
It was quite a technical project, because the veneer is set back the runners are set back and therefore set back on the drawers, all little details which need thinking about. Ensuring sufficient strength within the island to prevent sagging was a major consideration.
I see now how you’ve set back a fill for the vertical gaps they being visible in the second image down, and obviously required to carry the slides. I don't see any horizontal ones, presumably because they’re not practical to include or not technically required. I’m guessing dirt and dust can still work its way into the drawers, which was one of my concerns. I do like the lack of pulls, but perhaps they’re yet to be fitted or not required because the drawers are on touch latch opening and self-closing undermount slides.
Thanks for the additional explanation, although I have to admit I'm still not overly enamoured of the gappy appearance around the drawers. However, that's just my opinion, and aesthetic opinions, as you know, are like anuses - everyone's got one. If the client's happy, and they pay you gladly, that's really all that matters as far as I'm concerned. Slainte.