What do horizontal bumpy lines on your fingernails mean?

Beaus: Beau's lines are actual ridges and indentations in the nail plate, muehrcke lines are areas of hypopigmentation without palpable ridges; they affect the underlying nail bed, and not the nail itself. Some cuases of beau's lines include hypocalcemia, coronary occlusion, or even some skin diseases. It could be caused by drugs or malnutrition as well. It could also just be a normal finding.

Can be stress: Lines or ridges across the nail can be indicators of life stresses, like severe infection, starvation, serious trauma, etc. It can also occur locally from injury to the nail.

Consider psoariasis: Especially nail has little pits too.