I'd like to know if there is any difference between "fan steps" or the ronde steps that I am doing on certain advanced variations of the Tango.
Yes, there is a difference. A ronde is by definition circular -- the word itself means "round" -- while a fan may be circular or straight. The primary characteristic of a fan is foot extension, i.e. you "fan" the foot outward from the body.
The main thing that sets apart the fan and ronde is independence of the leg. With a ronde, the circular path of the foot is caused by a circling of the leg independently of the body. A fan, if it is circular, would be caused by the entire body turning with the leg held in a fixed position (e.g. forward, sideways or back). However, not all fans are circular.
The technique of many fans, particularly in American style Tango where the action is staccato, is not actually circular at all. It may appear round to an observer, but it's an illusion. The path of the extending foot is actually straight. The "round" appearance is due to the swiveling of the supporting foot while the free foot is extending straight out.
I should point out also that the body *can* turn during a ronde. In fact, most rondes are caused initially by turning the body. Typically the body stops turning once the ronde is underway (with perhaps a moment of overlap, depending), but that's not a defining characteristic, either. Were you to keep turning while the leg was circling, it would still be a ronde. As long as the leg is circling on its own, it's a ronde. If you were to hold the leg in a fixed position relative to the body while turning, then it would be a fan (round variety).
I hope that clears it up for you.
Regards,
Jonathan Atkinson
www.ballroomdancers.com