What does An eye for and eye mean?

It means to get revenge. like if someone breaks your favorite toy and you want to get even so you break their favorite toy.

The phrase "an eye for an eye"is a quotation from Exodus 21:23-27 in which a person who has taken the eye of another in a fight is instructed to give his own eye in compensation. At the root of the non-Biblical form of this principle is that one of the purposes of the law is to provide equitable retaliation for an offended party. It defined and restricted the extent of retaliation.