Recently, in multiple hotels, we paid for a double bed but got two smaller beds near each other instead. The two beds can move apart during the night, if you sleep on the middle. Should we complain? Is two twin beds near each other considered a double bed? It feels a little cheap and not correct.
I think “double bed” means that the room can accomodate two people sleeping side by side and not much more. The bed is not guaranteed to be as large as you might be used to (especially if you come from North America) and can come in many forms.
In Western/Southern Europe, I would expect only one bed, larger than a single bed but not huge. In some countries in Central Europe, it's really common to have two single beds side by side, with their own separate bed linen or, often, two single mattresses set side by side on a single bed frame. I know people in Germany (married couples) who have that at home. They wouldn't think of that as cheap or surprising in any way. There would however be some way to at least fasten the two beds together, though.
In fact, I have recently stayed at a mid-range German hotel where I got a very nice room, very spacious with all the amenities, a pillow menu, this sort of things. The bed was larger than usual and very comfy… but still came with two separate mattresses and a split between the two people sleeping in it.
International hotel chains might have a more specific terminology but I would not assume that to be universal.
I find I find this fairly common. It makes sense from the hotel's perspective because it allows them to convert a room fairly quickly from one that accommodates two people in one bed to one that accommodates two people in two beds.
I only wish that it were more common to have some sort of latch or other device to hold the beds together in case someone is lying in the middle.
Since you mentioned this is Romania, I found this guide for you.
It says that a double room can have accommodate for 2 people, with 2 beds (joint or separate).
The matrimonial is the one that has the big bed rooms, so it might have been a simple case of lost in translation.
Hotels normally have a mix of double (rooms with double beds) and twin (rooms with two beds), and will sometimes convert twin rooms into doubles by pushing the beds together.
You can normally ask when checking in if you specifically want a room with a double bed, as they'll normally give you one if they have one available.