The concrete panels were precast in the factory before being transported to the construction site.

precast 是由前缀 pre-（表示"预先"）和动词 cast（浇铸、成型）组成的复合动词，字面意思是"预先浇铸成型"。在建筑行业中特指"预制"构件，即在工厂预先制作好建筑部件再运到现场安装。