Think of it a little like Disney has their seasons. Unlike
DVC where you can reserve your villa for as little (1-day) or as much (how many points you have) days, for any time of the year you'd like (pay more points or fewer points), many (actually most) other timeshares have a 7-day week as the standard length of stay.
Fixed weeks are the same week every year. For example you have the 26th week of the year, every year. You don't make reservations at all. That's your week, already set-aside for you.
Floater weeks are when a week is not a fixed week, but is assigned to a specific season, a season when you can use your week, but you still have to call and reserve your week. The price (initial purchase) of the week will be higher or lower depending on what season it's in.
Just to make it simple, suppose there's a resort at a ski area in Colorado. Suppose also they have three-seasons: Winter (Prime season), Summer (Middle Season), and Step Season (Spring and Autumn).
If you purchased a floater week (High season), you would schedule your week during the high Winter season. You paid more for the right to have your week during prime skiing season. It would still be first come first serve on who got which week during the season (Just like who gets a Christmas reservation DVC)
If you purchased Step Season, you could schedule your week in the Spring or the Fall, but not in the Winter or the Summer.
In terms of DVC, it would be as if there were different levels of points: Points that could only be used in Adventure Season, Points that could only be used in Magic Season, and so on.
Hope this helps
