The word gravlax comes from the Scandinavian word gräva/grave ("to dig"; modern sense "to cure (fish)") which goes back to the Proto-Germanic *grabą, *grabō ("hole in the ground; ditch, trench; grave") and the Indo-European root *ghrebh- "to dig, to scratch, to scrape", and lax/laks, "salmon".
During the Middle Ages, gravlax was made by fishermen, who salted the salmon and lightly fermented it by burying it in the sand above the high-tide line.
Fermentation is no longer used in the production process. Instead the salmon is "buried" in a dry marinade of salt, sugar, and dill, and cured for between twelve hours and a few days. As the salmon cures, by the action of osmosis, the moisture turns the dry cure into a highly concentrated brine, which can be used in Scandinavian cooking as part of a sauce. This same method of curing can be employed for any fatty fish, but salmon is the most commonly used.