“完饭”不是一个正式的词，它常常是“吃完饭”的一部分。

"完饭" is not a formal word; it is often part of "吃完饭" (finish eating).

这里的“完”表示动作做完，“饭”是我们吃的东西。

Here, "完" means the action is completed, and "饭" is the food we eat.