The term "variable speed" is in reference to the air handler or furnace fan motor or blower motor and while they are variable speed motors they are not variable speed in the true sense. Residential models are designed to use the variable speed to run at several pre-set speeds somewhat just like any other air handler or furnace. The difference is both in the motor and in how it gets up to that speed and how it slows back down or stops.  

Read more info at http://www.asi-heating-airconditioning.com/About_Variable_Speed.html