ground zero
noun
in sing.
1- the point on the earth's surface directly above or below an exploding nuclear bomb（核弹的）爆心投影点。
1.1
- figurative a starting point or base for some activity〈喻〉起点; 基础：
if you're starting at ground zero in terms of knowledge, go to the library.
如果你的知识是从零开始, 那就去图书馆吧。
1.2
Ground Zero
the site of the World Trade Center in New York, destroyed by terrorists on 11 September 2001（2001年9月11日被恐怖分子撞毁的）纽约世贸中心废墟。