Oxford dictionary is not a good source when it comes to food. Two quick examples:

According to the dictionary, a pizza must be round and have both tomatoes and cheese.

>a dish of Italian origin, consisting of a flat round base of dough baked with a topping of tomatoes and cheese, typically with added meat, fish, or vegetables.

And mole is apparently expected to contain chocolate (most do not)

>a highly spiced Mexican sauce made chiefly from chilli peppers and chocolate, served with meat.

>All the recipes I saw were literally named “potato terrine (pavé)”, so I assume they’re used interchangeably

That seems to be a common mistake on recipe spam blogs, but it's certainly a bizarre way to describe a dish that doesn't even vaguely resemble anything else you'd refer to as "terrine".