LDL

Etymology

An initialism for "low-density lipoprotein," named for its low physical density in the laboratory. That lightness reflects its makeup: a large load of fat relative to protein makes the particle less dense than its counterpart.

noun · /el-dee-EL/
Low-density lipoprotein, the particle that carries cholesterol to tissues and, in excess, into artery walls.
What it names
The "bad" carrier on a blood panel — the number to keep down — though it does a job the body genuinely needs.
Example
The statin was prescribed to bring his LDL down, since it was the fraction driving the plaque in his arteries.
Related idea
LDL delivers cholesterol to the body’s cells and, in surplus, builds up in artery walls, while HDL carries it back toward the liver for removal — the "bad" and "good" labels track this direction of traffic, not any intrinsic evil in one molecule.