It’s a fair point, I’ve never even thought about that. I think it’s just something that’s awkwardly come about because there was an early broad categorisation of lipoproteins by density, and then there a subsequent need to divide those species even further by density.

I tried to come up with a corollary but the best I have is “jumbo shrimp”. Sigh.

I don't know what it is chemically, but why is that naming confusing? Some tortoises are in the family Giant Tortoise. Within that group some are smaller than others. A "small giant tortoise" is not so confusing? A video card can be mid-range. It can also be upper-mid-range or lower-mid-range. I assume similar of LDL; within the group "LDL" there is some variation in size and density; the smaller denser parts of the range have properties which make them worth talking about as a sub-group.

It's a term people use, e.g.

"Small Dense Low‐Density Lipoprotein Cholesterol Is the Most Atherogenic Lipoprotein Parameter in the Prospective Framingham Offspring Study" - Hiroaki Ikezaki MD, Elise Lim PhD, L. Adrienne Cupples PhD, Ching‐Ti Liu PhD, Bela F. Asztalos PhD, and Ernst J. Schaefer MD; Journal of the American Heart Association - https://www.ahajournals.org/doi/10.1161/JAHA.120.019140