Donburi is a bowl of plain, cooked rice with some other food on top of it. Some of the most popular varieties are gyudon (stewed beef), katsudon (tonkatsu), tendon (tempura), oyakodon (chicken and egg), tekkadon (tuna) and kaisendon (raw seafood).
Especially gyudon became famous through the “fastfood” chain Yoshinoya, which has branches all over the map.