The confusion arises because the common name 'rabbit' is often used to describe a hare. The two are different in many respects and are in different genera. For a fairly comprehensive description of similarities and differences see http://www.diffen.com/difference/Hare_vs_Rabbit

What I learnt is: Hares are bigger, have longer ears (longer than the nose if you bend them to the front) and don't dig holes like rabbits do. I don't know how close relatives they really are. There should be different species of either of them in the world so maybe the characteristics given above are not quite exact. I saw a pet rabbit "Deutscher Riese" that was surely bigger than a normal hare and also had long enough ears and no chance do dig a hole in its cage...