A thick, clear, slightly sticky jelly made from petroleum, rubbed on the skin to protect it or stop it drying out — on cracked lips, dry hands, a baby's bottom, a small cut, or a runner's feet to stop rubbing. Strictly it is a brand name, so careful writers use a capital V; but almost everyone now uses it as the ordinary word for the stuff, whatever brand is in the tub, in the same way people say Band-Aid or Xerox. The general name is 'petroleum jelly' or 'petrolatum', which is what you see on the label of cheaper versions. It is a mass noun: 'some Vaseline', 'a bit of Vaseline', never 'a Vaseline'. There is also an informal verb use — 'she vaselined her lips' — but it is uncommon and safest avoided in writing. One more use worth knowing: photographers and film people talk about a 'Vaseline lens' or a shot 'smeared with Vaseline' to mean a soft, blurry, dreamy look, because that trick really was done by putting jelly on the lens.