The classic timeshare product involves ownership; vacation clubs offer an alternative.
In the traditional property market you can either purchase your home or rent it. In the timeshare world buying timeshares is equivalent to purchasing your home, whereas vacation club rental is equivalent to renting it.
Why would you want to rent rather than buy? One reason could be the law of the land. Mexico law, for example, prohibits non Mexicans from ownership real estate in Mexico. Therefore, while a Mexican might own a specific unit-week in a resort, the American will purchase a right-to-use vacation club membership. Basically, this is a hedge against inflation by locking in your annual vacation at today's prices.
Often, however, vacation clubs offer more than a traditional timeshare. The membership may involve multiple locations; travel to and from the vacation site might be included and the membership might include specific resort activities such as boating.
A good example is the Marriott Vacation Club, which offers a choice of more than 50 locations in the USA (e.g. California, Florida, Hawaii etc.) and around the world (e.g. France, Spain, Thailand etc.) and a choice of vacation packages (golf, ski, beach etc.) and special offers when you can purchase at a discount during the limited time offer availability.