A fixed week is a set week in a set unit that you will occupy every year. The value of this ownership is that you will know which unit you will be using and where you will be going. If you decide not to use the week you can make it a "floating week" for that year by depositing it into the exchange system. You will pay an exchange fee to do this.
A floating week is determined differently at every resort and you need to make sure if the week is floating the entire year or if there are seasons that it is available. Floating allows you the option of calling to schedule your week without paying a fee. It is still based on availability. If you are not using it at your home resort then you will need to schedule a week with the resort and deposit the week with the exchange company.
A flex week means that your week is fixed unless you call to exchange it. This allows you the priority of using a certain unit but the privilege of exchanging within the resort during a certain period without paying a fee.