Lox isn’t lox and nova isn’t nova.
When people say lox, they really mean nova (“Nova Scotia” salmon) even though it isn’t always from Nova Scotia like it used to be.
Anymore, delis and food stores don’t seem to have actual lox. So we use the term loosely and everybody is really talking about and eating only nova these days. But years ago, you could get lox or nova and you had to specify which you wanted. Even some real delis today still offer both. So it is still worth knowing the difference.
A cautionary note: Lox is extremely, almost inedibly salty. It is an acquired taste and that is why most people understandably eat only nova and why the word lox has changed in connotation to refer to the type of smoked salmon that people actually eat.
Instead of trying to explain the difference, let me link to an expert in this helpful story from Bon Appetit :