What it is
Vitamins and minerals added back, usually because refining removed them.
Why your biology objects
Synthetic isolates that bypass the food matrix — folic acid, for instance, needs liver conversion the natural folate in greens doesn't, and excess can mask a B12 deficiency. Fortification is the label's written apology for what processing took out. (When it's iodine in salt or D in milk, that's a real public-health win, not an apology.)