What is considered abandonment of a child in the state of Florida?

If the child is left with no care or supervision.
If they leave the child with friends or relatives or an ex it is not abandonment.

This is an often confusing issue to people. It would help to explain why you are asking. I suspect it wasn't because you know of a child who was abandoned, but one where one parent has left and is not much of a part of the child's life.

Child Abandonement, as noted, is a criminal offense where a child is left without any adult supervision.

But, abandonment MAY be used as grounds to get something else. So please explain the background for why you are asking so we can help further.