VLDL, IDL, LDL, and HDL refer to lipoprotein density, which determines their separation in a lab gel.

“so what do those names mean anyway vldl IDL LDL HDL they all refer to another feature of the lycoproteins that is distinct from the APA lipoprotein that wraps around them which is their density so if you think about a high school experiment where you take various different substances and you put them into water you might notice that you can separate how they would float now water is kind of a bad example of how that works because things are typically binary behaving in water either they're sink or they're going to float but I think that gives you a conceptual understanding of the difference in density density is mass over volume and a higher density object relative to a lower density object will sink versus float so if you take all of those lipoproteins that I mentioned all of the APO B ones all of the APO a ones and you put them in a certain type of gel in the lab you can see a separation of them based on their density”

“again this is a historical artifact of how lipoproteins were discovered and named first of all hdls are much smaller I would say you know in the neighborhood of one-fifth to one tenth the size of an LDL and of course much yet smaller than triglyceride Rich lipoproteins you know lipoproteins have lipid as I mentioned earlier lipid floats so lipids create buoyancy to particles and the way lipoproteins were discovered is that when you subject plasma to spinning the lipoproteins spin to the top and they spin to the top at different rates under different forces the low density lipoproteins have more lipid or bigger more lipid they spin to the top more easily the high density lipoproteins still have lipid they do spin but they don't spin quite as quickly or easily so they're higher density than the low and then in another artifact of sort of the history Peter after low density was discovered something even lighter that spun up even more easily was discovered and of course if low was already taken so that had to be called very low and so there's the very low density lipoproteins that you've also talked about at length and then finally the chylomicrons the huge ones that come from the intestine they're just so light and so buoyant that instead of calling them very very very low they were just given the name kylo microns”