[GateKeeper]

You sound quite well informed about timeshare. The flexibility of certain packages has increased in a lot of cases where resorts are part of a larger collection and your interest can be shifted from one resort to another as resources permit, and your particular package allows.
A float week is just that, it can happen during a particular block of time during the year. Price usually dictates which weeks will be apart of your allowed block or blocks of time, the more you pay for your timeshare, the more aligned your block(s) is to key vacation periods for that area. A "red" "float" week in Tahoe, for instance, would cost a lot more than a "white" "float" week there when there's no snow on the ground, but still a beautiful place to visit.
As for trading your week, there are a number of exchange companies that, for a fee, allow you to participate in a trading program. Based on the "value" of your timeshare, you can "bank" your week with one of these exchange companies and then choose from available slots that others have also banked. There are fees and other considerations that you need to understand before basing your decision to exchange your week, but for th most part it is a fairly straight forward process.