牛肉 is beef (牛 is cow, and 肉 is meat). 丸 is ball (as in pellets or pills).
Sometimes it's 牛肉球 (ngàuh yuhk kàuh in Cantonese, niú ròu qiú in Mandarin), where the third character also is ball but as in planet, which is star ball 星球 (xīng qiú) or in sports: 小球 (síu kàuh) is small ball and refers to sports like ping pong and badminton, while 大球 (daaih kàuh) is large ball and refers to sports like basketball and soccer.
The name is sometimes prefixed with 山竹 (sāan jūk in Cantonese, shān zhú in Mandarin), which refers to the bedding under the meatballs, typically tofu skin, that raise the meatballs above their juices.
Steamed meatballs made out of finely ground beef is a [Cantonese dish] and standard dim sum fare.