A slang meaning of zoo is a place or situation marked by "confusion or disorder," or sometimes "chaos and unrestrained behavior." The interaction between Jerry and Peter in the play is certainly confusing, and the behavior at the end could be classified as "unrestrained."

On some level, playwright Edward Albee is using the word zoo as an analogy for the confrontation between Peter and Jerry. Since Jerry announces to Peter that he has just come from a literal zoo, and that something had happened to him there, it's natural to assume to that the title refers to the traditional definition of zoo, as a zoological garden. Several critics, however, believe that Albee intends the slang definition; still others perceive it as having dual meaning, a non-risque double entendre. Therefore, there is no clear-cut consensus on the reason for the title.

The most immediate reason the play is called "The Zoo Story" is that Jerry announces that he's been to the zoo when he first shows up. His story is a zoo story, and that starts a lot of the play's action in motion.

There are other less obvious /more symbolic reasons as well. Jerry lost his parents; many animals in zoos (especially older zoos) are without full family structures, and Jerry fights for territory like an animal. The characters in the play are trapped and lonely, like zoo animals. Animals play a part in discussions.