Calvados (or "calva") is a cider brandy only made from hard cider (and sometimes perry), protected by an AOC.
(an appelJack might contain some grain alcohol).
Cider must be made from fruits from orchards with a dominant variety of apples rich in phenolic compounds (bitter, or bittersweet, or sweet flavor). Those apples are quite different than the ones eaten. Whereas for an Apple jack, they are often the same.
"Calvados" comes, from Normandy, France (it is actually the name of a sub region of it) while "lambig" is its counterpart on the Breton side.
(Calvados is also used to make a "pommeau" drink : calvados + apple juice ).

The hard cider is distilled, sometimes twice. Then this brandy is aged in barrels (generally for 2 years but sometimes several dozen years). As it ages, it will soften and the apple flavours get more complex aromas of butter, vanilla, baked apple, licorice or woody …

Finally, the proportion of alcohol is reduced by adding pure water. (These steps became almost systematic when taxation became based on the alcohol level). Calvados must be at least 40% but some are still 55% (mostly the country side ones, under the counter ones).

Inhale the Calvados for a long time with caution (without breathing too deeply) to appreciate the aromas. In the mouth, get only a small amount not to be "burned" and to appreciate the balance, as well as once swallowed.

Old Calvados are appreciated in tulip glasses called "pointu" (because of their shape - "pointu" means sharp). Connoisseur therefore used to order a "pointu" at the end of the meal.

When the bottle is opened, if it is stored in a humid place the calvados will tend to soften (and become more alcoholic and tannic in a dry place).

Several more specific AOCs exist such as Calvados Domfrontais (minimum 30% pear) or Pays d'Auge (maximum 30% pear).

A "canard" (duck) is a piece of sugar dipped in a rest of Calvados.
A "coffee-calva" is a habit that tends to disappear.