The book To Kill a Mockingbird has nothing to do with killing a mockingbird - why?

The book,'To Kill a Mockingbird' does not mean literally killing a Mockingbird, it is a metaphor for innocence.

It is explained in the book that mockingbirds do not hurt anything and are innocent creatures. They should therefore not be shot at or killed. The symbolism there has to do with the race relations and loss of innocent life and innocence that the book addresses.