Earlier quoted context omitted.
We think that everything is made of things but we forget that everything is mostly made of nothing, and it's the gaps between things that make it all be. See also: atomic size vs distance between atoms in any structure, on perceptual levels the visual saccadic movement and how much the brain fills in the gaps. Nothing is quite something after all.
I hate this phrase because how do you even define "made of nothing" or "gaps between" when talking about objects as fuzzy as electrons, and how would you define where something "is" or "isn't " other than interactions? If an electron cloud is interacting with another electron cloud why do we say that space is empty? Because the measured radius of an electron is so much smaller than we observe?
The electron doesn't actually have a measured radius (in our current theories). QFT describes it as point-like excitation of an underlying quantum field. The only connection between our quantum theories (that is really just slightly hand wavy math) and reality is that our theories can predict the statistics of observing a particle or interaction in a given state. So maybe a slightly more coherent explanation is that for a given region between atoms in solid matter, the probability of observing an electron (or any particle) is extremely small. Its like a quantum mechanical cat who's territory extends across mountains and forests, you're probably not gonna stumble across it on any given day, unlike a (quantum) house cat that lives in someones apartment. More generally there are no big "lumps" in the wave-functions, it's very thinly spread like too little butter on toast.