"Main dish" is the term used in Engpsh to refer to the main course of a meal. The term comes from the traditional three-course meal structure that includes an appetizer (or starter), main dish, and dessert.
Examples:
"What's the main dish for dinner tonight?"
"I ordered a steak as my main dish."
Translation:
"今晚的主菜是什么？"
"我点了一份牛排作为主菜。"