The author's archive of animations is very pleasing: https://bleuje.com/animationsite/2024_1/

Moore Curve [1] is a sequence of curves that ends up filling a square as the sequence goes to infinity, thus asymptotically mapping [0,1] to [0,1]^2. (phrasing might not be mathematically correct)

So, my intuition tells me that what the site creator did is take the 4th Moore curve (which has 256 "corners") in the sequence, then spread 256 points on the [0,1] interval and map the later into the former. The output points then serve as cores for the Voronoi diagram [2].

"Adding holes" in the 256 input points thus means to creates gaps in the 256 input points, possibly at regular interval. The animation happens when points slide from adjacent from the gap into the gap. I can't find the exact logic of which point moves when. However, all points move at the same time when there are exactly 128 holes (i.e. 128 points on the curve), and there are three batches of points that move one after the others when there are 64 holes (thus 3 batches of 64 points moving).

[1] https://en.wikipedia.org/wiki/Moore_curve

[2] https://en.wikipedia.org/wiki/Voronoi_diagram

Hint: if you're on mobile, zoom out and go to the bottom left corner. The page appears broken at first, but it's just the layout, at least on iOS.

Is there a description or some explanation of what this is?

A really well explained video regarding voronoi diagrams and animations : https://www.youtube.com/watch?v=mEyWZmIBSqU

That's hypnotic