Whats this white discolouration on my nail?

either what the other people said, or if you wear nailpolish all the time, and then take it off your nails will sometimes be yellow from lack of oxygen.Whats this white discolouration on my nail?
If it's like a spot or something, it can be some sort of lack of calcium. I know there's a proper term for it-I just forgot what it was. It's like calcium de-something.Whats this white discolouration on my nail?
I've heard that its a calcium deficiency and possibly dehydration. Its a bruise on your nail.

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