When I first arrived, I had a system for keeping everything straight. The bus is just a bus but if you have to pay more then it's a special route bus. The vehicle that goes on the road but has a wire at the top is a trolley. The vehicle that is attached on top but has its own track is the tram. Now I don't have to think about it too hard. :)
I like the tram because it goes nice and slowly and I don't get motion sickness. On the other hand, if you want to get somewhere fast, you're out of luck. Another feature of the tram is that the route sometimes goes across different metro lines and is therefore more convenient than going all the way down one metro line and up another.