Our car was trapped in the deep snow, and we had to wait hours for a tow truck.

was 是 be 动词的过去式，表示被动语态或状态。 trapped 是动词 trap 的过去分词形式，trap 的意思是"困住、陷入"，这里表示"被雪困住"的状态。 was trapped 是被动语态结构，表示"被雪困住"这一被动状态。