what does it mean to be Salt born

[Knight]

does mean we are born from the ocean? or does it mean we are born from the dust of the earth?

[Klendt]

Well, it has to do with the phrase "salt of your brow". In ancient (and classical, and pre-modern...) times, salt was among the most valuable commodities a man could earn. Its value in preserving foodstuffs was objective and practical, so it became the de facto backing of most currencies. A soldier being "worth his salt" was a literal statement, as their wages were paid in salt - where we get the term SALary.
So in this setting, Salt has an otherworldly power over life, and debatably IS life. Not coincidentally, the sea has a lethal abundance of it, and there's something twisted about it.
ALSO not coincidentally, the Island appears to have a profound bond to the sea, and the terrors from the deep make themselves readily apparent there.
However, this capital S salt, this mystical substance, seems to be nearly mythological - the subject of rumor and folklore and hushed whispers. As far as the mortals know, their salt goes directly to the gods. The manipulation of salt is therefore seen as something profane and evil, and its manipulation, Alkymancy is held in the same sort of fear and contempt as raising the dead in some other setting.

On the island, the salt takes a physical form and can be manipulated directly. Your labors and hard work and guts directly create this salt. If someone were to want to actually engage in Alkymancy in order to pervert the laws of nature, here's definitely where they'd do it.

In a nutshell, to be Saltborn is to be a mortal being that has to work hard and spend itself in order to create power and worth.

[AlmightyDunkle]

We are born of the salt, made men by the salt, die by the salt.
By the Nameless Gods fear it.

[C(r)ap]

To be born of light - to be a true god. To be born of salt = undeads in dark souls (power and humanity at the cost of killing everything and absorbing it's salt) Naturally, every saltborn has salt that cannot be lost when they die. So instead, the only last you can loose, is the one you stole. The nameless god absorbed so much salt, thinking he will be worthy of becoming a being of light, however, he is just a mere saltborn like our player.