The noodle soup topped with tempura to make tempura udon is udon.
Udon are thick, chewy Japanese noodles made from wheat flour. They are commonly served in a mild broth based on dashi, soy sauce, and mirin, then finished with toppings such as scallions, fish cake, tofu, or prawn tempura. Adding tempura—especially shrimp or kakiage, a mixed fritter—creates tempura udon.
The topping can be placed directly in the soup, where its batter gradually absorbs broth, or served alongside it so the crust stays crisp. Regional styles vary, including differences in broth color and seasoning. Eastern Japan commonly uses darker soy sauce, while western versions often use lighter soy sauce.
Tempura udon is distinct from tempura soba. The former uses thick wheat noodles, while the latter uses soba, traditionally associated with buckwheat. Ramen and pho are also noodle soups, but they belong to different culinary traditions and are not what the Japanese dish name specifies.