“Gyu (Beef)” + “Don” = “Gyudon.” Seasoned and cooked beef is over the rice in the bowl this time. This is one of the Japanese traditional menus, but it became a huge hit when a franchise came to Japanese fast food market.
(“Yoshinoya” is the most popular franchise in “Gyudon” market in Japan.)
(Ajinomoto created frozen Gyudon.)
Since Yoshinoya established its “Gyudon” franchise, most Japanese think of “Gyudon” as “Gyudon from Yoshinoya!” Also, “Gyudon” is the food when you are in a hurry or to go cheap. Traditionally, the Japanese cooked “Gyudon” at home. I don’t know if it is still the case in Japan now, though…