What does it mean when you have white thick lines on the nails?

Leukonychia: Leukonychia white nails. Consider hypoalbuminaemia or chronic renal failure. May be familial. Transverse leukonychia, or multiple parallel white lines, are thought to be due to manicuring but may also arise in association with beau's lines. Beau's lines are depressions across the fingernail. These lines can occur after illness, injury to the nail, and when you are malnourished.