Thomas,
I struggled with this too and eventually found enough references to consolidate this into a couple simple sentences.
Free Float which is the amount you can delay an activity without delaying the next one. An example answer described Free Float as the amount of time that a schedule activity can be delayed without delaying the early start date of any successor or violating a schedule constraint.
Total Float which is the amount you can delay an activity without dealing the whole project. An example answer described Total Float as the amount of time that a schedule activity can be delayed or extended from its early start date without delaying the project finish date or violating a schedule constraint.
Project Float which is the amount that you can delay a project without delaying the next project. Project Float can also be the amount the critical path can be delayed without delaying the project past its constrained finish date. An example test answer said that Project Float is not in the PMBOK guide and describes it as the slack of the project itself in terms of affecting other completion dates external to the project.
