It's an alveolar tap (Wikipedia if you want more), which is very similar, if not identical, to the 'd' and 't' sounds in American English, but in many foreign languages where it occurs (and in archaic pronuncations of RP British English) it is used to represent an 'r'.
Rolled r is different, technically called an alveolar trill. With the tap sound, the tongue makes contact just once (hence the name!), while in a roll/trill the tongue vibrates against the contact point. (The alveolum, where the tongue makes contact for both these sounds, is that ridge on the roof of your mouth, a little ways behind your front teeth. Feel it? That's where your tongue should touch when you say Norwegian "r"!)