The phrase "nail bed" refers to the skin and tissues underneath your nails where they are attached. It is the part of your finger or toe that supports and holds your nails in place.
Instead, try drinking water and eating protein regularly, which will help keep nail beds hydrated and will produce strong nail plates. (mindbodygreen.com)
It's very sheer; even at three coats, I can still see my whole nail bed. (wacie.com)
Wasn't that nice of her... whatever nail beds are. (housegoeshome.com)