Bedding labels outside of the US are sometimes very different.

Double vs Twin
In the US, we’re familiar with the idea of a DOUBLE bed being the logical step up from a twin bed. Its width is that of two twin beds and the same length as a single twin bed. Pretty simple concept. The only real nuance to it is that in the US we sometimes use the term “full” interchangeably with “double”.
Forget all of that when you’re dealing with Europe. You’ll see double beds all over European hotel and travel sites, but they don’t mean the same thing at all. Matter of fact, they don’t even always mean the same thing from European country to European country.
The most common DOUBLE bed scenario in a European hotel room is that you’ll find two twin beds pushed together, usually sitting atop the same platform. Just imagine two mattresses atop one box spring (or whatever platform is being used, since box springs aren’t as common). This is what “DOUBLE” means in most countries. It’s not referring to the mattress size description- it’s literally referring to two separate mattresses.

Most hotel sites and travel sites will show “TWIN” rooms as the alternative to “DOUBLE” rooms. Understanding European twin beds is a little more straightforward than understanding doubles.
It’s not uncommon to see European TWIN rooms laid out with the beds right next to each other. And by right next to each other, I mean right next to each other. Sometimes the amount of space in between can be measured in inches. It’s also likely that the layout will have the beds at a more comfortable distance. It can be unpredictable.

“TWIN” rooms are intended for guests who are sharing a room but not a bed.
“DOUBLE” rooms are intended for guests who are sharing both a room and a bed.

From https://roundtript.com/european-beds/