Lox is salmon cured in salt. In general in this country, lox is made with salmon from the Pacific Ocean. Nova, on the other hand, is generally made from Atlantic salmon (the Nova being short for Nova Scotia), and is cured in salt and smoked. It is considered the finer of the two preparations and is more expensive. You will come across many people who will tell you that lox is also smoked. You can ignore them or not, as you choose.

Gravlax, or gravadlax, on the third hand - and which you did not ask about - is cured in salt and sugar with other flavorings (generally dill, pepper, and brandy or aquavit).