Heavy cream is a North American generic term for creams that have at least 35-36% butterfat in them.
They can be whipped and because of the higher-fat content, aren’t as likely to curdle in sauces as lower-fat creams.
Heavy cream is a bit too heavy for coffee (though you can thin it with milk or water in a pinch). It is good for pouring over fruit or cooked cereals.
Substitutes
For whipping, there is no cream substitute for Heavy Cream unless you go for a higher fat content and use Double Cream.
For sauces or in cooking:
EITHER
1/3 cup (2.5 oz / 75 g) unsalted butter, melted and cooled a bit plus 2/3 cup (5 oz / 160 ml) milk = 1 cup (8 oz / 250 ml) heavy cream
OR
any of these: Evaporated Milk, a high fat yoghurt such as Greek Yoghurt (regular yoghurt will curdle), Sour Cream, Ricotta Cheese, Crème Fraîche, or puréed unsalted Cottage Cheese.