Donburi/丼 is a Japanese dish consisting of rice in a bowl, topped with something.
There are many different types… beef is gyudon/牛丼.
Chains like Matsuya, Sukiya and Yoshinoya specialise in this cheap dish.
Businessmen are often seen eating gyudon alone in those chains because it is super cheap.
It’s Japan’s fast junk food
Chicken and egg is oyakodon/親子丼.
Eel or unadon/うな丼 is another favorite, especially in summer.