Gravlax is a specialty sugar, dill and salt cured salmon from Sweden. The smoky salmon is part of a traditional smorgasbord. Gavlax should be sliced thin and serve atop dark bread.
Look for gravlax in a good deli if you have one. If you want to buy online then you can purchase several versions on Marky's gourmet store. Trade Joe's carry's other types of thinly-sliced smoked salmon. If you'd like to make your own at home there are many good recipes online such as this one from the New York Times, Mark Bittman's Gravlax.
If you don't have Gravlax then the closest substitute would be: