As far as most people are concerned, the term skeletonization is an informal way of describing the process of removing structurally superfluous material from a mechanical or structural element.
Refer to yesteryear's Liberator to the right. You're looking at the bottom plate. As you can see, there's a lot of area that is just airspace. The big cutouts toward the bottom of the image look filled in by that off-white material, but that's just a 1mm polycarbonate sheet (which turned out to be a very effective solution).
Ironically, we went on to determine that we could have afforded to cut even more material away.
This concept applies to just about every design. If you are using any metal, which you absolutely should be, you have to be deliberate about what structures you are choosing to make the strongest. Because that stuff is heavy.
As an oversimplified rule of thumb, aim to have support that is perpendicular to places that you expect to get hit a lot. If you want to get really nitty-gritty about it and impress that (strictly hypothetical) beautiful brown-eyed Raytheon recruiter at the career fair, you can delve into Finite Element Analysis (FEA). There's a lot of YouTube content about this that can explain it far better than I can.