1.zoo的意思是“动物园”,是正式用语zoological garden的缩略词,指饲养各种动物并向公众开放参观的园地,多用在口语中,在美国口语中也可喻指“拥挤而乱哄哄的地方”。
2.the Zoo特指“伦敦动物园”,也可指一个国家中有代表性的动物园,如芝加哥动物园、上野动物园等。

A zoo is a place where live animals are kept in captivity for the public to see.动物园是圈养动物以供公众观看的场所。
Two gorillas have escaped from the zoo.两只大猩猩从动物园里逃跑了。
There are many animals in a zoo.动物园里有许多动物。
They are going to the zoo.他们要去动物园。
We took children to the zoo to see the monkeys.我们带孩子们去动物园看猴子。
Modern zoos are much better than they used to be.现代的动物园比过去的好得多。
They spent the summer visiting zoos and parks.夏天他们游览了动物园和公园。
Let's go to the Zoo.咱们去伦敦动物园吧。
His sister works at Beijing Zoo.他的姐姐在北京动物园工作。
The students are all moving today.It's going to be a zoo.学生们今天都在搬家,这儿会搞得乱哄哄的。

at the zoo, in the zoo
这两个短语都是“在动物园里”的意思。表示“在动物园里(饲养)”时要用介词in,其他情况下则用at。例如:
There is a panda in the zoo.动物园里养着一只大熊猫。
I had a ride on an elephant at the zoo.在动物园我骑在大象背上兜了一圈。