Lox was traditionally only made from the belly of salmon, although other parts of the fish are now also used. The salmon is salt-cured or brined but never cooked or smoked, so it has a very silky, rich texture and translucency. Lox is the traditional topping of bagels with cream cheese and is most often served thinly sliced.

There are two other versions of lox where the preparation methods do vary a bit:
Nova Lox: This lox, which comes from Nova Scotia, is actually cold-smoked after the curing or brining process.
Gravlax: Gravlax is the Scandinavian preparation of lox, where lots of fresh dill and spices such as juniper berries and pepper, as well as some liquor such as aquavit or brandy, are additional ingredients used during the curing process.

Smoked salmon is a much more generic term than lox. Smoked salmon can be made from any part of the fish, and it starts with salt curing or brining, just as in lox.  The next step is where smoked salmon is different from lox. The salmon can be covered in spices or a dry rub after curing, then smoked in one of two ways:
Cold-Smoked Salmon: The salmon is slowly exposed to smoke in about an 80°F environment for a few days. The salmon doesn’t get cooked, so the flesh of cold-smoked salmon stays very moist and silky and has a beautiful translucent pink color. Cold-smoked salmon has a similar texture to lox, but has an additional layer of smoky flavor. It is also a common topping for bagels and cream cheese and is usually sold thinly sliced.
Hot-Smoked Salmon: The salmon is smoked with heat in the same way meat gets smoked. The fish gets cooked all the way through and ends up with a firm, flaky, and drier texture, but it also has a distinct smoky flavor. When shopping for hot-smoked salmon, it looks very similar to a piece of cooked or grilled salmon.

Source:   Kitchn

All lox is smoked salmon, but all smoked salmon is not lox.

Smoked salmon is a blanket term for any salmon: wild, farmed, fillet, steak, cured with hot or cold smoke.

Lox refers to salmon cured in a salt-sugar rub or brine (like gravlax). Nova is cured and then cold-smoked (unlike lox or gravlax). There’s also hot-smoked salmon, which is cured, then fully cooked with heated wood smoke.

Now, to acknowledge the purists. Real, authentic lox is made from only the belly portion of the salmon. Yup, like pork, the belly of the fish is typically the richest, fattiest and most succulent portion. Cured and smoked, it’s saltier and more…uh…”aromatic” than its milder non-belly counterpart, and if you’re lucky enough to try it on a bagel with cream cheese, it’s hard to go back. When you buy lox anywhere other than an old-school appetizing counter, even if it’s clearly labeled “lox,” what you’re almost certainly getting is simply smoked salmon. And frankly, that’s fine by us.

Source:  Food Republic:

Therefor, in the interest of convenience and expense, we just use plane old Costo smoked salmon.  Accompany it with pumpernickel bread, cream cheese, diced red onion, mustard, and capers.  Good to go!